Tropical Update – Early Sat AM

The somewhat rare situation is setting up right now that may allow two tropical cyclones (tropical storms or hurricanes) to be in the Gulf of Mexico and threatening the continental U.S. at the same time. However, there is a lot of uncertainty with the two storms. The newly-designated Tropical Storm Marco is located just off the Yucatan Peninsula (SW of Cuba), and T. S. Laura is the one in the Caribbean to the east, centered just east of Puerto Rico.

Marco is better organized this morning, with USAF C-130 hurricane hunter aircraft finding flight-level winds around 41 knots, and thunderstorms developing near the center. Most of the thunderstorms associated with Laura are to the east of its low pressure center, and that will make intensification slow for a while. It is the condensation and release of latent heat by thunderstorms that lowers the surface pressure underneath those storms, so until the storms line up with the center, strengthening is difficult.

Marco is expected to move northwest toward the Texas Coast by Tuesday. Even though the waters in the Gulf of Mexico are very warm this time of year, the upper-level trough of low pressure that has been keeping our weather unsettled here in Alabama lately will produce wind shear that will keep Marco from becoming fully vertically-stacked the way an efficient hurricane would be.

Then there is Laura. The NHC track has been shifted to the left. That is good news if it holds, as there would be land interaction through Monday (Puerto Rico, Hispaniola, Cuba), keeping the storm weaker. This thing will be moving over a lot of undisturbed, warm water (84-90 F) for the next 3-5 days, and by the time it gets into the central Gulf late Monday, wind shear will be decreasing. There is still track uncertainty in the computer models, as shown below. Most now take it toward Louisiana by next Wednesday night.

The track staying south until Monday then turning northwest indicates that the models are counting on the Bermuda High spreading west into Alabama, Georgia, and the eastern Gulf ovet the next few days, with the upper trough weakening and moving into the Ohio Valley. This would allow the storm to go around the high then move north between it and the trough next week. Tropical systems generally find the path of least resistance to go north (their large-scale role in nature is to redistribute heat upward and northward).

(Images from pivotalweather.com, annotated by me)

There is also the unknown effect of the “Fujiwhara effect” where two cyclones interact if they get close enough together. They can start to rotate around each other or even converge. That is a very complex process and impossible to forecast at this point.

It will be an interesting week along the Gulf Coast. Anyone with family, friends, or property along the Gulf Coast, pretty much anywhere in the US, but especially from about Pensacola westward, needs to pay close attention to this developing situation in the coming days.

Dr. Timothy A. Coleman

Consulting Meteorollogist

Coleman and Knupp, LLC

http://www.colemanandknupp.com

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