Two Atlantic tropical rainmakers were threatening to become tropical cyclones on Wednesday, June 29. One disturbance, designated 95L by the National Hurricane Center (NHC), was spinning off the Texas-Louisiana coast. Another disturbance, Potential Tropical Cyclone 2 (PTC 2), was speeding across the southern Caribbean. 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 U.S. interest is 95L. Satellite images on Wednesday afternoon showed a modest area of heavy thunderstorms to the northeast of a broad circulation a few hundred miles off the South Texas coast, but there was no well-defined low-level surface circulation. Radar images showed that 95L’s low-level bands of precipitation to be poorly organized, with a few heavy showers affecting the Texas coast near Freeport.
Upper-level winds from the southwest were creating moderate wind shear of 10-15 knots, pushing dry air into the heart of 95L, and its environment was only moderately moist (relative humidity of 60%). One thing working in 95L’s favor were very warm sea surface temperatures (SSTs) of around 29-29.5 degrees Celsius (84-85°F), with even warmer waters closer to the coast. Steering currents are expected to take 95L to the west at roughly 5 mph through Wednesday night, with a more northwesterly track occurring Thursday, bringing the center ashore along the central Texas coast on Thursday.
Given the weakness of the surface circulation and the expected persistence of wind shear, there is little chance that 95L will undergo rapid intensification. Its main effects on the Texas and Louisiana coasts – heavy rains of 2-4 inches – are likely to be more beneficial than problematic, as the region has been dealing with moderate to severe drought. But some localized flooding is possible, especially in parts of coastal Texas, where isolated rainfall totals could approach or exceed five inches this week. A side benefit of this system is a slight break from the intense heat of this month, currently on track to be the warmest June on record in the Houston-Galveston area.
In its 8 a.m. EDT Wednesday tropical weather outlook, NHC gave 95L 2-day and 5-day odds of development of 40%. A hurricane hunter aircraft is to investigate 95L Wednesday afternoon.
PTC 2 near tropical storm status
As of 11 a.m. EDT Wednesday, tropical disturbance Potential Tropical Cyclone Two (PTC 2) was speeding west at 21 mph along the northern coast of South America toward the ABC islands (Aruba, Bonaire, and Curacao). PTC 2 was centered about 130 miles east-southeast of Curacao, with top winds of 40 mph. 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. The system appeared well-organized on satellite images, and radar from Curacao showed a decent structure, with a few spiral bands bringing heavy rains to the ABC islands and the northern coast of South America. On Tuesday night, PTC 2 generated a wind gust of 74 mph in a severe thunderstorm that hit Grenada.
The atmospheric and oceanic conditions around PTC 2 will favor strengthening over the next several days: light wind shear (below 10 knots), warm ocean temperatures of 28 degrees Celsius (82°F), and a moist midlevel atmosphere (relative humidity 60-70%). PTC 2 has been hampered from developing a closed circulation because of its rapid forward speed; the recent slowdown in its motion (from 30 mph early Wednesday to 21 mph late Wednesday morning) should help it close off a center and become a tropical storm by Thursday morning. Interaction with the coast of South America will slow development until the storm moves into the southwestern Caribbean on Thursday, though. The main short-term threat will be heavy rains, with 3-5 inches predicted for the ABC islands and 4-6 inches for the northern coast of South America.
PTC 2 will have a better chance of strengthening once it clears far northern Colombia and moves through the southwestern 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 near hurricane strength, as predicted by NHC. PTC 2 is expected to survive crossing Central America and become a tropical storm in the eastern Pacific by early next week. In its 8 a.m. Wednesday forecast, NHC gave PTC 2 2-day and 5-day odds of development of 80% and 90%, respectively. The next name on the Atlantic list of storms is Bonnie. A hurricane hunter aircraft is scheduled to investigate PTC 2 on Wednesday afternoon.
Yet another tropical wave to watch
On the heels of PTC 2, a vigorous tropical wave located in the central tropical Atlantic near longitude 45°W on Wednesday afternoon was moving west-northwest at 10-15 mph. Satellite images showed that this wave was quite disorganized, though a few of GFS and European model ensemble members developed this new tropical wave into a tropical depression by the time it moves through the Lesser Antilles on Friday evening.
Steering currents will take the wave on a more northerly track than PTC 2, into the northeastern Caribbean, where wind shear is projected to be notably stronger than that faced by PTC 2. Very little model support indicates the new wave will survive intact by the time it reaches Puerto Rico and/or the Dominican Republic on Sunday. In its 8 a.m. Wednesday tropical weather outlook, NHC gave the wave 2-day and 5-day odds of development of 10% and 30%, respectively.
Bob Henson contributed to this post.
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