Tropical Wave in Central Atlantic not an Immediate Threat, but Should be Watched

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Watching A Wave in the Central Atlantic – Still Waiting for the Atlantic to Get Active

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Tropical Storm Fernand Forms – Bigger Threats Likely from Eastern Atlantic in September

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Development Possible in Bay of Campeche – Eastern Atlantic Still on Track to Get Active

A couple areas of disturbed weather have developed in the Caribbean and Gulf of Mexico over the last day or so, in response to the unstable pattern in the region. A surface trough developed in the northern Gulf of Mexico a couple days ago, and is bringing rain to the central gulf coast. As I mentioned yesterday on Facebook, although mid-level rotation has been evident, low-level convergence is focused southwest of the main area of thunderstorms, which is keeping the feature decoupled, and development appears unlikely as it moves generally westward along the north gulf coast over the next couple of days. The feature may bring some much-needed rain to coastal Texas.

To the south, a vigorous tropical wave moved into the Yucatan Peninsula last night, and an area of low pressure has developed near the mid-point of the wave axis over land today, designated Invest 95L by the NHC. There appears to be a closed circulation, which may emerge over the extreme southern Bay of Campeche by tomorrow. Given its excellent structure already, development of a tropical depression or storm may ensue immediately after moving over the water if it has enough room away from land. A deep-layer ridge to the north will keep 95L on a generally west or WNW track, and very little time will be spent over water before moving back into Mexico. Thus, the system is expected to be mainly a rainfall threat for Mexico.

Looking to the east, the tropical Atlantic remains quiet for the moment. The ITCZ is much farther north than normal, and low-level wind patterns are very favorable for the development of tropical waves. What is lacking right now is vertical motion to generate thunderstorms. The MJO is expected to move into phase 1 by most of the models during the next week or two, and this should provide a “boost” to the eastern Atlantic beginning by the end of this month and the beginning of September. Once the air finally becomes unstable enough, we should start to see tropical storms forming from tropical waves and ITCZ lows.

A pattern like this can accelerate activity rapidly. If the missing ingredient is added, we could quickly go from no storms at all to multiple storms simultaneously. The global models are starting to see this likely uptick in activity, with the GFS, CMC, and ECMWF now all hinting at development east of the Caribbean in the 6-10 day time frame. Below is the ECMWF forecast for Day 10, showing one or two disturbances trying to develop. This is still in the long-range, but this is the first time this year that the reliable ECMWF has shown tropical development in the central-eastern Atlantic. Take this as another sign that the peak of the season is here, and it won’t be long before our first hurricane forms.

It’s starting to get pretty late for our first hurricane, but in a pattern like we have this year, once the first one forms, it may uncork a burst of storms that doesn’t stop for multiple weeks. Four named storms typically form during the month of September. I think we are likely to see a more active than normal September this year. Be prepared in case any of these storms come your way.

No Immediate Development Threats in the Atlantic, but Active Period Coming by the End of August

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92L Likely to Remain Weak – Heavy Rain for East Gulf Coast – Light Rain Possible for Texas

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92L Over the Yucatan – Unlikely to Strengthen Much in the Gulf of Mexico, But Will Send Heavy Rain Northward

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*Updated 7pm Wednesday* – Watching Western Caribbean and Gulf of Mexico for Potential Development – Rainfall the Main Hazard

Update 7pm EDT Wednesday:

Invest 92L continues to organize in a gradual fashion today, as expected. However, the system is somewhat decoupled, with the low-level wave axis to the west of the main area of convection and the mid-level vort max. This means that 92L may not be able to develop into a tropical depression prior to running into the Yucatan Peninsula during the next 12-24 hours. Either way, the impacts will be the same for central America, with heavy rain and potential flooding being the primary hazards. If 92L doesn’t develop before hitting the Yucatan, it will have another chance on the other side in the Gulf of Mexico. However, the trough to the north will likely string its moisture out towards the north gulf coast, and if the system is unable to consolidate, we may never see it develop significantly. However, it is prudent to wait for 92L to clear the Yucatan before judging how it may behave in the gulf. The forecast philosophy presented in yesterday evening’s post remains essentially unchanged today, so I am leaving the video and forecast graphic below for this evening due to time constraints. Current information, satellite loops, and model tracks for 92L can be found at the storm information page.
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Tropical Development Possible Near Yucatan Later This Week – Flooding Currently Main Threat

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Tropical Development Possible Next Week in the NW Caribbean or Gulf of Mexico

There are currently no significant tropical disturbances in the Atlantic, but one is likely to form in the western Caribbean next week, and will have a good shot at developing into a tropical cyclone. The originating feature is a broad, deep-layer wave of low pressure located east of the lesser Antilles, most pronounced at the 500mb level in 18z GFS analysis. This is the system I mentioned in my video on Sunday as a potential threat next week. Although there are currently few clouds associated with this feature, that should change in a few days. The wave will move westward through the Caribbean, and once west of 75-80W, it will serve as a brake on the trade wind flow coming in behind it from the east. This will cause air to pile up and rise in the western Caribbean, and widespread thunderstorms will likely result. This will likely happen in 5-7 days, resulting in at least a weak area of low pressure in the western Caribbean.

As the low moves northwestward, it will be moving into a progressively more favorable environment as ridging balloons aloft over the NW Caribbean and an upper low backs away to the west, illustrated by the GFS Day 7 upper wind forecast. The WNW to ESE orientation of the jet stream to the north over the U.S. will likely allow upper ridging to continue ballooning into the Gulf of Mexico over the disturbance, an environment conducive for tropical development. None of the main global models show significant development of this disturbance, but given the favorable environment it will be moving into, I think it will be a threat to develop in the vicinity of the NE Yucatan Peninsula. The latest runs of the GFS have begun hinting at a tropical storm forming in the Gulf of Mexico, beginning to support this idea. The GFS and CMC ensemble means have also recently begun to show an increasingly wet NW Caribbean in about a week from now, indicating heavy precipitation associated with a strong tropical disturbance.

If a tropical storm does form in the NW Caribbean or southern Gulf of Mexico, its future track will be of obvious interest. The pattern a week from now is forecasted to feature a washed out (stalled) front draped over the southern U.S., evident as deeper blues in this forecast image. The upper trough that brought this front in is likely to stall near the eastern seaboard and leave a weakness over the eastern gulf through which our disturbance could move on a northeastward path towards Florida. However, given the washed out nature of the front with high pressure building behind it, it may be difficult for a disturbance near the Yucatan Peninsula to recurve into Florida. Also, the 500mb pattern for storms near the Yucatan Peninsula that end up hitting east of the Mississippi typically features a strong trough coming down from the Midwest, not a trough that is in the process of leaving the SE US like what is forecasted for next week. Thus, a more likely path to me currently seems to be westward or northwestward into the western Gulf of Mexico towards northern Mexico or southern Texas. However, considerable uncertainty exists, as this forecast is for at least a week from today, and the track of the disturbance may be influenced by whether it even develops into a storm or not. Details about the future of this system in the Gulf of Mexico will be better known in 5-7 days when it is trying to develop in the western Caribbean.

The concept chart below illustrates my overall thoughts for this system next week. I will likely post a video update in a couple of days, especially if the computer models begin to support development of this system.