The forecast for the upcoming week is both complex and simple at the same time.
We start the week off with a hot and humid day today, thanks to high pressure located over the Atlantic (more on that in a bit). Temperatures will get into the upper 80s and 90s across the region this afternoon. When you combine that with dewpoints generally in the 60s, it’ll feel like it’s in the mid 90s during the afternoon. Clouds will quickly start to stream in at night, making for a rather warm and muggy evening.
As we head into Tuesday, we turn our eyes to the southwest and Tropical Storm Isaias. The combination of a trough of low pressure approaching from the west and that high pressure over the Atlantic will steer Isaias into the Carolinas late tonight or early Tuesday. After that, it will start to quickly move north-northeastward, likely passing west of the region late Tuesday night or early Wednesday. Most of the heavy rain will be located west of the track, but we’ll still have some showers and tropical downpours around here late Tuesday and Tuesday night. The storm should also be weakening and passing far enough to our west to spare us from any significant wind issues. It’ll be breezy, with some gusts to 40 mph or so possible, especially along the South Coast, but overall, it really shouldn’t be too big of a deal. Once again, the hype will be likely worse than the reality.
By Wednesday morning, Isaias is out of here and skies will clear out, with drier air settling in as high pressure builds into the region. That high should remain in place for the rest of the week and into the weekend, with seasonably warm temperatures and comfortable humidity levels.
Monday: Partly to mostly sunny, breezy, and hot. High 86-93.
Monday night: Becoming mostly cloudy with a few showers possible. Low 67-74.
Tuesday: Cloudy and becoming windy with showers likely, some of them may be briefly heavy. High 79-86.
Tuesday night: Mostly cloudy and windy with showers ending, skies may start to clear late at night. Low 67-74.
Wednesday: Becoming partly to mostly sunny. High 81-88.
While crossing the Bahamas on Saturday, Hurricane Isaias weakened to a tropical storm, but it remains a threat to much of the East Coast.
As of 2pm Sunday, Tropical Storm Isaias was centered about 45 miles east-southeast of Vero Beach, Florida, moving toward the north-northwest at 9mph. Maximum sustained winds were near 65 mph, and should remain near that level for the next day or two, with some fluctuations in strength possible. Tropical Storm Warnings are in effect from Jupiter Inlet, Florida to Surf City, North Carolina, with a Tropical Storm Watch north of Surf City to Duck, North Carolina, including Albemarle and Pamlico Sounds. A Storm Surge Watch is in effect from Edisto Beach, South Carolina to Cape Fear, North Carolina.
Isaias moved across the Bahamas as a hurricane late Friday into early Saturday, before weakening to a Tropical Storm Saturday afternoon. The combination of southwesterly wind shear and some dry air due to Saharan Dust contributed to the weakening. Isaias is maintaining its strength this afternoon despite the presence of more wind shear.
Isaias should continue to head towards the north today, in between a large area of high pressure of the east, and an approaching trough of low pressure from the west. As the trough continues to move towards the East Coast, it will help turn Isaias more towards the north-northeast and eventually northeast. On this track, Isaias will parallel the coast of Florida and Georgia today and tomorrow, then likely make landfall in either South Carolina or North Carolina late Monday night or early Tuesday. Once inland, Isaias will continue northeastward, and although it will weaken a bit, it should maintain some strength as it moves up the coast, as it starts to transition into an extratropical storm.
Storm surge will be a threat along the Carolina coast, near and east of where the center makes landfall. A surge of up to 4 feet above normal tide levels could result in some coastal flooding. Strong winds will also be a threat, mainly east of the storm’s center. Winds have been gusting as high as 50 mph along the Florida coast this afternoon. As it moves northward, some strong winds will be likely across eastern North Carolina as the storm moves inland, and possibly across eastern New England late Tuesday into early Wednesday as the system moves across the Northeast.
By far, the biggest threat with Isaias is heavy rainfall and the resulting flooding. Some bands of heavy rain have moved across parts of Florida, and that will continue through tonight. Rainfall totals of 1-3 inches are possible across parts of Florida and Georgia over the next 24-36 hours. As you head north, heavier rain is likely from the Carolinas into the Mid-Atlantic states and the Northeast, mainly along and west of the storm’s track. Rainfall totals of 3-6 inches and locally heavier are likely, which will produce flooding in many areas. The storm’s relatively quick motion will preclude even heavier totals. East of the storm’s track, rainfall will be much lighter, with many places likely seeing less than 1 inch.
Elsewhere, we’re keeping an eye on a tropical wave located a few hundred miles east of the Leeward Islands. Conditions could become favorable for it to develop into a tropical depression in a few days. Model forecasts show it heading northwestward, staying north of the Caribbean over the next few days. By mid-week, most forecasts show it stalling out about midway between Bermuda and the Bahamas. It does not look like a threat to any land areas at this time.
Tropical Storm Isaias strengthened into a hurricane early Friday as it pulled away from the Dominican Republic and headed towards the Bahamas. Meanwhile, the threat to the East Coast is starting to increase.
As of early Friday morning, Isaias was centered about 45 miles southeast of Great Inagua Island in the southeastern Bahamas, and was moving toward the northwest at 18 mph. Maximum sustained winds have increased to 80 mph based on recent data from reconnaissance aircraft. A Hurricane Warning is in effect for the northwestern, central, and southeastern Bahamas.Tropical Storm Warnings remain in effect for the entire Dominican Republic, the north coast of Haiti and the Turks and Caicos Islands. A Tropical Storm Watch is in effect for the east coast of Florida from Ocean Reef to Sebastian Inlet.
The short-term forecast for Isaias is rather simple. It will continue to move toward the northwest across the Bahamas while gradually slowing down. Waters remain very warm in this area (29-31C), and wind shear shouldn’t be that strong, which will allow Isaias to strengthen a bit more over the next day or two.
Once Isaias gets into the northwestern Bahamas, things get a bit trickier. A large high pressure area in the western Atlantic, and a trough of low pressure moving into the eastern United States will help to steer Isaias more towards the north-northwest, and then north, and eventually northeast. Exactly when those turns occur is critical to the forecast.
The current forecast calls for Isaias to make the northward turn east of Florida, sparing the Sunshine State from the worst of the storm. It may be close enough to bring some gusty winds and heavy rain to east-coastal Florida over the weekend, which is why the Tropical Storm Watch has been issued. That watch will likely be extended farther north on Friday. After that, it will head towards the Carolina coastline late Sunday into Monday. This is where the uncertainty is magnified.
If the Western Atlantic high is stronger than currently expected, or if the trough moving into the East is sharper than the models are currently showing, then Isaias will continue northward, likely moving across eastern North Carolina. A weaker high or flatter trough, would allow for a more northeastward movement, which could allow Isaias to only graze the Outer Banks or possibly even miss them completely.
Once the storm is beyond the Carolinas, there is more uncertainty with its track. Again, a more northeastward motion would bring the storm out to sea with little additional impact to any land areas. A motion that is more toward the north-northeast or even north would increase the threat to parts of the Northeast, including New England, for late Monday or Tuesday. As this point, coastal residents from Florida to New England should all keep tabs on the storm’s progress, as it could impact a large stretch of coastline this weekend and early next week.
If Isaias does make its way to New England as a hurricane, it would be extraordinarily early in the season for an impact up here. The earliest that a hurricane has ever made landfall in New York or New England was when Hurricane Belle slammed into Long Island with 90 mph winds on August 9, 1976. Hurricane Arthur passed just offshore of Nantucket on July 4, 2014. While it did not make landfall, it made for a rather wet and cool holiday, especially across Cape Cod and southeastern Massachusetts. Statistically, the most likely time for a hurricane to hit New England is between the middle of August and late September. Of the 18 hurricanes that made landfall in New England or Long Island since 1851, 16 of them have done so between August 19 and September 27. Since 1951, 36 storms have made landfall in New York or New England as tropical storms or hurricanes, but only 5 have done so before August 5.
An Unnamed Tropical Storm crossed Long Island on May 30, 2008 with winds of 45 mph.
An Unnamed Tropical Storm made landfall new Newport, RI on July 21, 1916 with winds of 70 mph.
Tropical Storm Cindy made landfall near Falmouth, MA on July 11, 1959 with winds of 60 mph.
Tropical Storm Agnes made landfall near New York City on June 22, 1972 with winds of 65 mph.
Tropical Storm Beryl crossed Nantucket with winds of 50 mph on July 21, 2006.
If it seems like we’ve been talking about this storm for a while, it’s because we have. Isaias was well-advertised by the models for almost a week before it finally developed over the eastern Caribbean on Wednesday. We even mentioned it in our Weekly Outlook early Monday morning. It has produced wind gusts of up to 60 mph and heavy rain that produce flooding across parts of the Virgin Islands, Puerto Rico, and the Dominican Republic. Wind gusts as high as 54 mph were also reported in the Turks and Caicos Islands Thursday evening.
We’ve been mentioning for several days now that a wave in the Atlantic needed to be watched for development. It isn’t a tropical cyclone yet, but it appears to be a matter of when, not if, it will become one.
While the system has a broad circulation and plenty of thunderstorm activity, it has not become a tropical cyclone as of yet. Until that circulation tightens up into a well-defined low-level center, it is just a tropical disturbance. The National Hurricane Center has dubbed it “Potential Tropical Cyclone Nine” as of midday Tuesday. This designation allows the issuance of Tropical Storm Watches and Warnings for many of the islands in the northeastern Caribbean, including Puerto Rico and the Virgin Islands. The center of the system is estimated to be about 500 miles east of the Lesser Antilles. It is moving toward the west at 23 mph, and has maximum sustained winds of 40 mph. The expectation is that the circulation will tighten up and the system will become a tropical storm in the next 24 hours. If it does, it will be given the name Isaias (pronounced ees-ah-EE-ahs). This has already led to many in the media and on the internet saying that it is the earliest “I” storm on record. This is true, but it ignores the fact that at least 2 of the storms we’ve had so far this season should not have been named.
Air Force reconnaissance aircraft are out investigating the system this afternoon, trying to determine its strength and whether it has developed a low-level center yet. Once that center does develop, we’ll have a better idea of where the system may go. Right now, the forecast is for the system to cross the Lesser Antilles early Wednesday, then move across the Virgin Islands and Puerto Rico Wednesday night and early Thursday. However, if recon finds that the center has developed in a spot that is not near where the Hurricane Center currently thinks it is, that will obviously have implications on the track of the system. Changes to the track will also have implications for how strong to system gets. As we’ve been saying for a few days now, until the system actually develops, all model forecasts for the system are suspect.
Obviously, minor details could have major implications om the system’s future, but right now, it looks like it will track near or just north of the Greater Antilles. How close to passes to the islands will determine it’s strength. The closer it is, the more likely it is that the mountains of Hispaniola disrupt the circulation and keep it weak. The farther away, the more likely it stays mostly over water and strengthens while possibly impact the Bahamas along the the Turks and Caicos Islands. We’re not even going to speculate beyond that, because even forecasting this far out is more speculation than we’d like. We’re highly aware that many models, especially the ensembles show a threat to the East Coast, literally anywhere from Florida to Nova Scotia. We’re not ruling that out yet, but again, it is pure speculation at this point. We’ll say it again – once the system actually develops, we’ll start to have a better idea of where it’s going and how strong it may be. For now, it’s just something to keep an eye on.
Heat and humidity continue across the region for a couple more days before relief arrives on Wednesday.
A ridge of high pressure remains in control, so stifling heat and humidity will remain in place until Tuesday. Today looks to be the hottest day, with temperatures well into the 90s. A few places could reach 100, but triple-digit heat shouldn’t be widespread. It will be very humid as well, sending the heat index well above 100 across the region, but dewpoints may actually drop a bit during the afternoon. Tonight will be downright uncomfortable without air conditioning, as low temperatures will only drop into the middle to upper 70s in many areas, and some urban areas, especially Boston, may not drop below 80.
Tuesday will start off very warm and humid, so it won’t take much to send temperatures above 90 once again, but clouds will also start to increase in the afternoon as a cold front approaches the region. This front may produce a few showers and thunderstorms late in the day and at night. Some of these storms may produce some heavy downpours and gusty winds, but we’re not expecting widespread severe weather.
The front slides offshore early Wednesday, then high pressure builds in for the rest of the week and into the weekend. It be a bit cooler, but still near to a little above normal for the end of July, but the more noticeable effect will be that it is drier, with dewpoints only in the 50s to lower 60s.
Monday: Sunshine and some high clouds around, hot and humid. High 92-99.
Monday night: Clear to partly cloudy. Low 72-79.
Tuesday: Sunny early, then clouds move in with some showers and thunderstorms possible late in the day. High 90-97.
Tuesday night: Showers ending during the evening, though possibly lingering for much of the night near the South Coast. Low 67-74.
Wednesday: Lingering clouds along the South Coast early, otherwise becoming partly to mostly sunny and not as humid. High 85-92.
Thursday: Sunshine and some afternoon clouds. High 83-90.
Friday: A mix of sun and clouds. High 81-88.
Saturday: Partly to mostly sunny. High 81-88.
Sunday: Partly sunny. High 82-89.
Finally, we’ll mention the tropical disturbance in the Central Atlantic, since the hype train is already getting set to leave the station. Yes, there are a few models that show a potential threat to the East Coast in about 7-10 days. These should be treated the same as model forecasts in January that show a raging blizzard 7-10 days out. The probability of it happening is still fairly low. The system itself hasn’t even become a tropical depression yet. That may occur later Monday or Tuesday. If (when?) it does, we’ll write a blog post about the storm and it’s future. For now, it has our attention, but that’s it.
Between the Atlantic and the Central Pacific Ocean we have three named storms, and all of them will threaten land areas this weekend.
We’ll start again with Tropical Storm Hanna, since it is the most immediate threat to land. As of 8pm EDT, the system was centered about 190 miles east-of Corpus Christi, Texas, moving toward the west at 10 mph. Maximum sustained winds were near 50 mph and additional strengthening is likely. Hanna could become a hurricane before making landfall in south Texas on Saturday. A Hurricane Warning is in effect for the Texas coast from Baffin Bay to Mesquite Bay, and a Storm Surge Warning is in effect from Baffin Bay to Sargent. A Tropical Storm Warning is also in effect from Baffin Bay southward to the mouth of the Rio Grande, and from Mesquite Bay northward to San Luis Pass.
A storm surge of 2-4 feet is likely near and to the north of landfall. and strong winds are also likely near the coast and a short distance inland near landfall, but heavy rain and inland freshwater flooding remains the biggest threat with this system. Slow-moving tropical systems have produced significant rainfall in Texas many times before, and while we’re not expecting 50+ inches like Hurricane Harvey produced a few years ago, widespread totals of 6-12 inches with isolated amounts of up to 20 inches are possible through early next week. To the north, rainfall of 2-6 inches will likely cause flooding from Austin and San Antonio over to Houston.
While Hanna is the immediate threat to the US, out in the Atlantic, Tropical Storm Gonzalo is a threat to the southern Windward Islands. As of 8pm EDT, Gonzalo was centered about 340 miles east of the southern Windward Islands, moving toward the west at 18 mph. Maximum sustained winds have decreased to near 45 mph. Drier air has taken a toll on the system, and will continue to do so. A Tropical Storm Warning remains in effect for St. Vincent and the Grenadines, Tobago, and Grenada.
Gonzalo’s future remains very uncertain. The official forecast calls for Gonzalo to restrengthen a little over the next 24 hours, then weaken and dissipate after moving into the eastern Caribbean. However, at this point, it is just as like that it weakens and opens up into a wave before it crosses the islands on Saturday. No matter what it does, it will bring some squally weather to parts of the southern Windward Islands on Saturday. We’ll also need to keep an eye on what the remnants of the system do as they move across the Caribbean. Conditions in the western Caribbean could be a bit more favorable early next week and the water is plenty warm, so regeneration is not out of the question.
In the Central Pacific Ocean, Hurricane Douglas is starting to slowly weaken after peaking as a Category 4 Hurricane on Thursday. As of 8pm EDT, Douglas was centered about 725 miles east-southeast of Hilo, Hawaii, moving toward the west-northwest at 18 mph. Maximum sustained winds have decreased to 115 mph, making Douglas a Category 3 storm on the Saffir-Simpson scale. Some additional weakening is expected on Saturday as Douglas moves over cooler waters. A Hurricane Watch has been posted for Hawaii County and Maui County, including Maui, Lanai, Molokai, and Kahoolawe.
The forecast track for Douglas has shifted northward a bit over the past 24 hours, but still indicates the potential for Douglas to impact Hawaii as a weakening hurricane on Sunday, though some models keep the center north of the island chain completely. Rough surf, gusty winds, and heavy rainfall are likely across the islands starting late Saturday and continuing into Monday. Rainfall totals of 6-12 inches and locally up to 20 inches may cause flooding in some areas.
Finally, we’re keeping our eyes on a tropical wave in the eastern Atlantic Ocean. The wave isn’t that organized right now, but as it crosses the Atlantic, conditions could become more favorable for development. In fact, many models do show this developing into a tropical cyclone towards mid-week, and possibly becoming a threat to the eastern Caribbean by late next week. Model forecasts 5-7 days out aren’t terribly reliable, but there are some that show the system becoming a threat in about 10-12 days to anywhere from Central America to the Gulf to the East Coast, to Bermuda, to a system that passes harmlessly out to sea. In other words, it’s WAY to early to speculate about a system that hasn’t even formed yet. Yes, it’s something to watch, but that’s about it right now.
Scheduling Note: Our Weekend Outlook will be published early Friday this week instead of Thursday afternoon as it usually is.
The tropics had been relatively quiet in the past couple of weeks, but we suddenly have 3 storms that are all threats to land.
We’ll start with Tropical Depression 8, since it is the most immediate threat to land. As of 11am EDT, the system was centered about 380 miles east-southeast of Port O’Connor, Texas, moving toward the west-northwest at 9 mph. Maximum sustained winds were near 35 mph. The system should continue on a general westward track for the next day or two, with some strengthening possible. As a result, a Tropical Storm Watch is in effect for the Texas coast from Port Mansfield to High Island.
While gusty winds and some rough surf are likely along the Texas coast, the biggest threat from this system will be heavy rainfall. Slow-moving tropical systems have produced significant rainfall in Texas many times before, and while we’re not expecting 50+ inches like Hurricane Harvey produced a few years ago, widespread totals of 3-6 inches with isolated amounts of up to 10 inches are possible this weekend. That would produce flooding in many areas.
While TD 8 is the immediate threat to the US, out in the Atlantic, Tropical Storm Gonzalo presents a threat to parts of the Windward Islands. As of 11am EDT, Gonzalo was centered about 885 miles east of the southern Windward Islands, moving toward the west at 14 mph. Maximum sustained winds are near 65 mph. A Hurricane Watch is in effect for Barbados as well as St. Vincent and the Grenadines.
Gonzalo’s future is very uncertain. The official forecast calls for Gonzalo to become a hurricane later today, then start to weaken after moving across the Windward Islands this weekend and into the eastern Caribbean. However, Gonzalo looks less organized on satellite photos today, and is fighting off some dry air aloft. There is a decent chance that the system could weaken or even open up into a wave before reaching the Windward Islands. How it develops over the next 12-24 hours will give us a much better idea of what the future holds for it.
In the Eastern Pacific Ocean, Hurricane Douglas continues to strengthen this morning, and could become a threat to Hawaii this weekend.
As of 11am EDT, Douglas was centered about 1335 miles east-southeast of Hilo, Hawaii, moving toward the west-northwest at 20 mph. Maximum sustained winds have increased to 120 mph, making Douglas a Category 3 storm on the Saffir-Simpson scale. Some additional strengthening is possible today before a weakening trend begins on Friday as Douglas moves over cooler waters.
Douglas is expected to only gradually weaken while heading towards the west-northwest over the next several days. On this track, Douglas is expected to pass close to or over parts of the Hawaiian Islands this weekend. Obviously which islands would be impacted and what the threats would be will depend on the exact track Douglas takes, as well as how quickly it weakens. At this point, gusty winds, heavy rainfall, and rough surf appear mostly likely for the Big Island, but the entire island chain could be impacted.
While Hawaii has been impacted by many weakening storms passing by the islands, a direct hit is actually fairly rare. Since 1871, only 3 hurricanes and 4 tropical storms have actually made landfall on the islands. The last system to make landfall in Hawaii was Tropical Storm Olivia in 2018. The last hurricane to make landfall in Hawaii was Hurricane Iniki in 1992.
Beyond these systems, there’s nothing on the immediate horizon. Some of the longer-range ensemble models are showing the potential for a wave to move off the the African coast and develop while crossing the Atlantic next week. This is still several days away, and while the likelihood of it happening is fairly low, we are getting into the time of year when some of these waves do start rolling off of Africa and maintain themselves while crossing the Atlantic. Just like in the winter when you’ll see Day 16 model images of a mega-blizzard for the Northeast, we’re already seeing people posting model images for a potential East Coast hurricane 2 weeks from now. Don’t buy into the hype. Until something actually develops, it doesn’t exist, let alone present a threat.
The 2020 Hurricane Season has had two themes so far: 1. Tropical Storms that aren’t really tropical. 2. Storms that fall into the “Blink and you’ll miss it” category. We’ve got another one out there, and this is squarely in category #2.
A disturbance that moved from the Gulf of Mexico and into the Southeast last week moved off the South Carolina coast on Wednesday. After sitting over the warm waters of the Gulf Stream, thunderstorm activity began to increase, and a new center of circulation developed Thursday afternoon. Air Force Reserve Hurricane Hunters investigating the system determined that it had a closed circulation (barely), and the system was designated as Tropical Storm Fay.
Fay is the 6th named storm of the season (Whether all 6 deserved to be named is highly debatable), and is the earliest we’ve ever had an “F” storm in the Atlantic. The previous record was held by Tropical Storm Franklin during the 2005 season, which developed on July 22. Despite the record start in terms of named storms, most of the storms have been short-lived and of little impact. Meteorologists use a metric called ACE (Accumulated Cyclone Energy) to determine the severity of a hurricane season. It takes into account how strong storms are, how long they remain strong, and how long they last. Despite having 6 named storms so far, the Atlantic has an ACE of 7.4 this season. While this is more than double the normal through July 10 of 3.1, it is exactly the same as the Western Pacific Ocean, where only 2 storms have formed so far this year.
While there are still a few minor details that need to be determined, Fay’s future is fairly clear. With a ridge of high pressure in the western Atlantic, and a trough of low pressure moving into the Great Lakes, Fay should head northward for the next 24 hours, hugging the Mid-Atlantic coastline. The official forecast from the Hurricane Center has Fay make landfall near Atlantic City later today, but a slight jog to the east will keep the center offshore longer, with landfall farther to the north. A Tropical Storm Warning is in effect from Fenwick Island, Delaware to Watch Hill, Rhode Island, including Long Island Sound. This includes southern Delaware Bay as well all of Long Island and southern Connecticut, and also New York City.
Fay currently has maximum sustained winds near 60 mph (Edit: Yeah, right), and little additional strengthening is expected before landfall. The storm is moving northward at 12 mph, and should pick up a little speed today. This track will keep most of the strongest winds offshore, but right along the coast winds will remain brisk. Sustained winds near 40 mph were reported along the Delaware coast earlier this morning.
Fay’s biggest threat will be heavy rainfall that could lead to flash flooding, especially from the Mid-Atlantic states into eastern New York and western New England. Much of this region has been dry for a few months, and drought conditions are beginning to develop. Some of this rainfall will help alleviate that, but too much rainfall too quickly will just run off and not help much at all. By the time Fay pulls away early Saturday, rainfall totals of 2-5 inches are expected from the Delmarva Peninsula into western New England and eastern New York, mainly along and just west of the expected track of Fay. Some isolated totals in excess of 6 inches are possible. Amounts will taper off the farther east or west you head away from this area.
Once Fay dissipates, there don’t appear to be any other areas that may develop in the next week or two. It’s still early in the season, and easterly waves will begin rolling off of western Africa soon, with the climatological peak of hurricane season still more than a month away.
The National Hurricane Center is tracking another system in the Atlantic, but the only threat it presents is to the Hurricane Center’s credibility.
Late Monday afternoon, the National Hurricane Center started issuing advisories on “Subtropical Depression Four”, which was centered a little more than 300 miles southeast of Nantucket. Their forecast calls for it to strengthen into a Tropical Storm tonight, at which time it would be given the name “Dolly.” The system should head eastward then northeastward, staying over open waters before it weakens and then, according to the forecast, becomes “extratropical”. Here’s the problem. It’s extratropical now, and has been the entire time.
To be considered a tropical or even subtropical system, it needs to be “warm core.” What that means, is that temperatures are warmest at the center of the storm, and cooler as you head away from the center. In some stronger hurricanes, like Dorian from last year, temperatures can be as much as 20 degrees warmer in the eye compared to just outside the eye.
Tropical systems also need warm water to feed them and help them strengthen. The threshold is generally accepted as 27C (80F) as the minimum needed for a tropical system to maintain itself and/or strengthen. This system is over the northern edge of the Gulf Stream, which is fairly mild, but water temperatures in the region are 25-26C, and quickly drop to 22-24C just to the east of the system’s current location. That’s not warm enough to sustain a “tropical” system.
Lastly, and this partially refers back to the first point we made about the system being cold-core, the storm itself is centered under an upper-level low pressure system. Tropical systems usually need an upper-level high pressure system over them, to help vent the rising air near the center. The stronger the high aloft, the more a tropical system will strengthen. A storm sitting under an upper-level low is the same as most of the storms that we see impacting us all through the year – extratropical. As you can see in the analysis below, there is a trough of low pressure extending southward from the system. It’s not quite a cold front, but close enough. Extratropical systems have fronts and/or troughs extending from them, tropical systems don’t.
Assuming this gets named Dolly, it will be our fourth named “tropical” system this year. However, only one, Cristobal, was ever truly tropical. Cristobal was a tropical storm when it moved into southern Mexico. When it moved back over the Gulf and headed towards Louisiana, it was already extratropical, even though the Hurricane Center didn’t declare it extratropical until it got into Iowa.
It’s been a running joke among meteorologists for years that if a system is over water and has a thunderstorm nearby, it’ll get a name from the “National Thunderstorm Center.” This storm is just further proof of that. With many forecasts for an active hurricane season, every system is going to get named to pad the stats and help verify that forecast. We’ve had colleagues joke that by the time this season is over, we’ll have gone through the entire name list and the Greek Alphabet. We not only agree with that sentiment, we even made a prediction elsewhere that “Tropical Storm Lambda” will produce 70 mph winds on Nantucket in late December while bringing 6-12 inches of snow to southern New England. As long as there’s a thunderstorm in the warm sector, it’ll get a name.
As far as actual tropical systems, none are forthcoming in the Atlantic for at least a week or two, thanks to several plumes of Saharan dust moving off the coast of Africa and across the Atlantic over the next several days. The dust is accompanied by very dry air, which suppresses thunderstorm activity.
After dumping feet of rain on portions of southern Mexico and Central America, Cristobal is now starting to take aim on the Gulf Coast.
Early Friday afternoon, Cristobal had strengthened back into a Tropical Storm and was located about 35 miles south-southeast of Merida, Mexico, moving toward the north at 12 mph. Maximum sustained winds have increased to near 40 mph. Cristobal should continue moving toward the north, with the center of circulation moving back over the Gulf of Mexico later today or tonight. Once that happens, the system should strengthen a bit more.
Cristobal is a bit of a lopsided system right now, with most of the rainfall along with the strongest winds all located east of the center of the storm. While some of the rainfall will eventually rotate around to the western side of the storm, the overall structure of the system likely won’t change much over the weekend. This has important implications that we’ll get to in a little bit.
As Cristobal moves away from Mexico tonight and Saturday, some additional strengthening is expected. The waters of the Gulf are very warm, which will help the storm intensify, but the presence of dry air aloft and some wind shear will act to inhibit significant strengthening. Cristobal should strengthen a bit more on Saturday, but at this time, it does not look like it will become a hurricane before approaching the central Gulf Coast Sunday night.
The current forecast calls for Cristobal to make landfall as a tropical storm along the coastline of Louisiana Sunday evening. A Tropical Storm Warning is already in effect for the coast of Mexico from Punta Herrero to Rio Lagartos, where tropical storm conditions are expected into Saturday. A Tropical Storm Watch has been issued from Intracoastal City, Louisiana to the Alabama/Florida border, including Lakes Ponchatrain and Maurepas. A Storm Surge Watch has also been issued from Grand Isle, Louisiana to Ocean Springs, Mississippi, including Lake Borgne, and also along the coast of Florida from Indian Pass to Arepika.
As we mentioned earlier, Cristobal is a bit lopsided, and this should still be the case as the storm moves inland Sunday night. That’s not to say that areas west of the center will escape without issues, but they shouldn’t be as problematic. There will still be some heavy rain, and wind gusts to 30-40 mph, but this isn’t anything the region hasn’t experienced plenty of times before. Near and east of the center are where the problems will become more numerous.
Cristobal should have sustained winds of 50-60 mph near the center at landfall, but these winds will only be experienced over a small area along the coast. The remainder of the area will likely have sustained winds of 30-40 mph, with some gusts to 50-60 mph. Along the coast, a storm surge of 2-4 feet will result in flooding of some areas, especially the low-lying locations near the Mississippi River entrance. By far, the biggest threat is heavy rain.
Rainfall totals of 4-8 inches are expected across a wide area, with isolated totals to 12 inches possible. This will lead to flooding across much of the region. Flood watches have already been issued. Parts of the Gulf Coast have actually been in a drought recently, but too much rain in a short period isn’t a good thing. Once inland, Cristobal should weaken and head northward, bringing heavy rain to parts of the Mississippi Valley and the Great Lakes early next week.
Tropical Depression Three formed in the Bay of Campeche Monday afternoon and strengthened into Tropical Storm Cristobal Tuesday afternoon. It made landfall along the coast of Mexico Wednesday morning, and has been drifting around southeastern Mexico and Guatemala for the past 48 hours. Cristobal has produced torrential rainfall, with 15-25 inches of rain reported across much of the region, resulting in widespread flooding. Another 3-6 inches of rain, possibly more, is expected across this region before the system pulls away over the weekend.