Two tropical rainmakers were flexing their muscles in the far northwest Gulf of Mexico and the far southeast Caribbean on Tuesday, June 28. One disturbance, designated 95L by the National Hurricane Center (NHC), was spinning off the Texas-Louisiana coast. Another disturbance became Potential Tropical Cyclone 2 on Monday southeast of the Windward Islands. Either system could become a named storm this week, but regardless of what they’re called, their heavy rains will affect a wide swath of coastline.
The system of more immediate US interest is 95L, a broad area of low pressure in the northwest Gulf accompanied by a persistent area of showers and thunderstorms (convection) at the tail end of a decaying cold front. Pockets of convection were pulsing around the broad low on Tuesday afternoon, but there was no sign of a low-level circulation. Top sustained winds were only around 25 mph.
95L is fighting strong southwesterly wind shear of 15-20 knots that’s pushing dry air into its heart, and its environment was only moderately moist (relative humidity of 55-60%). One thing working in 95L’s favor is very warm sea surface temperatures (SSTs) of around 30°C (86°F), with even warmer waters closer to the coast. A minority of the European and GFS model ensemble runs from Tuesday morning depict 95L developing into a tropical depression – or perhaps a weak tropical storm – as it drifts toward the Texas coast by late Wednesday or Thursday. Smaller systems like 95L can strengthen or weaken rapidly, but given the weakness of the surface circulation and the expected persistence of wind shear, there is little sign of 95L having powerhouse potential. In its 2 pm tropical weather outlook, NHC gave 95L a 40% chance of development in the next five days, with the same odds in the two-day range (implying that any development would be expected no later than Thursday).
The main effects of 95L on the Texas and Louisiana coasts – scattered downpours – should be more beneficial than threatening, since the region has been dealing with moderate to severe drought. Some localized flooding is possible, especially in parts of coastal Texas, where isolated rainfall totals could approach or exceed 7″ this week.
A side benefit of this system is a slight break from the intense heat of this month, which is on track to be the warmest June on record in the Houston-Galveston area.
PTC 2 likely to remain weak as it grazes South America
It could be a while before PTC 2 achieves its full potential as a tropical cyclone. As of 5 pm EDT Tuesday, June 28, the broad area of rotation within PTC 2 had yet to form a distinct low-level circulation, even though the system already has sustained winds of tropical-storm strength (40 mph). A hurricane-hunter pass on Tuesday afternoon showed that nearly all of PTC 2’s winds were easterlies, enhanced by the trade winds, as opposed to the more symmetric wind pattern one would see in a healthy tropical cyclone. A broad shield of showers and thunderstorms (convection) extended from east to west.
PTC 2 was centered about 210 miles of Trinidad at 5 pm EDT Tuesday, moving west at 23 mph. Heavy rains and squalls associated with PTC 2 were spreading across Trinidad, Tobago, and Grenada on Tuesday evening and will reach the ABC islands (Aruba, Bonaire, and Curacao) by Wednesday. Rainfall of 3″ to 5″ can be expected throughout these islands, where tropical storm warnings were in effect Tuesday night. Tropical storm watches were up for the Venezuelan and northeast Colombian coastlines.
The atmospheric and oceanic conditions around PTC 2 will favor strengthening over the next several days: light wind shear (below 10 knots), warm SSTs (27-28°C or 81-82°F), and a moist midlevel atmosphere (relative humidity 65-70%). However, it may be difficult for PTC 2 to form a sharp low-level circulation as it moves across the far southeast Caribbean, as the south side of PTC 2 will be interacting with the coastal landscape of Venezuela, especially on Thursday. It’s quite possible the system will remain a PTC, or perhaps become a weak tropical storm, as it dumps heavy rains of 4″-6″ along coastal South America. Such a coast-scraping trajectory would keep Venezuela mainly on PTC 2’s weaker side, which would help reduce the risk of destructive rainfall and major flooding, though localized floods are certainly possible. In its 2 pm Tuesday outlook, NHC gave PTC 2 a 70% chance of becoming a tropical storm by Thursday afternoon.
Assuming it holds together, PTC 2 will have a better chance of strengthening once it clears far northern Colombia and moves into the southwest Caribbean on Thursday and Friday. A majority of European and GFS ensemble members intensify PTC 2 late this week as it approaches the coast of Nicaragua, with a possible landfall on Saturday at hurricane strength, as predicted by NHC.
Yet another tropical wave to watch
On the heels of PTC 2, another vigorous tropical wave was located in the central tropical Atlantic near longitude 45°W on Tuesday afternoon, moving west-northwest. The fate of this wave will hinge in part on the influence of nearby PTC 2.
A substantial number of GFS and European model ensemble members develop this new tropical wave into at least a tropical depression by the time it approaches the Lesser Antilles around Friday. Steering currents will take this wave on a more northerly track than PTC 2, into the northeast Caribbean, where wind shear is projected to be notably stronger than that faced by PTC 2.
In its 2 pm Tuesday outlook, NHC gave this wave a near-zero chance of development through Thursday and a 20% chance in the 2- to 5-day window.
Jeff Masters contributed to this post.
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