92L near tropical depression status; Ernesto drenching Mexico

A tropical wave midway between Africa and the Lesser Antilles Islands (Invest 92L) has become well-organized, with satellite loops showing that a well-defined surface circulation formed around 9 am EDT. So far, 92L's heavy thunderstorm activity is limited, due to a large amount of dry air to the west and north that can be seen on water vapor satellite loops. However, heavy thunderstorms have recently increased near the new circulation center, and if current trends continue, 92L will likely be named Tropical Depression Seven later today. Wind shear is a light 5 - 10 knots, and the SHIPS model predicts that shear will remain light until Saturday morning, when the storm will encounter higher shear from upper-level westerly winds associated with a trough of low pressure. Of the six major computer models used operationally by NHC, only the NOGAPS model develops 92L, and not until Tuesday. The NOGAPS model did the best job of forecasting the genesis of Ernesto, though. There are some major timing differences between the models on how fast 92L will move. The GFS model predicts 92L will reach the Lesser Antilles Islands on Saturday, the ECMWF model has this happening on Sunday, and the NOGAPS model brings 92L though the northern Lesser Antilles on Monday. In their 8 am Tropical Weather Outlook, NHC gave 92L a 70% of developing into a tropical cyclone by Saturday morning. Residents of the Lesser Antilles should anticipate the possibility of another Ernesto-like situation, with tropical storm conditions affecting the islands Saturday through Monday.


Figure 1. Morning satellite image of Invest 92L.

Ernesto
Tropical Storm Ernesto is performing a tightrope act along the extreme southern edge of Mexico's Bay of Campeche, as the storm heads westwards towards its eventual doom over the mountains of Mexico. Ernesto made landfall Tuesday night at 11 pm EDT just north of the Belize/Mexico border as a Category 1 hurricane with 85 mph winds, weakened to a tropical storm with 50 mph winds while passing over the Yucatan Peninsula on Wednesday, but had enough time over water this morning to regenerate to a 70 mph tropical storm. Ernesto has a few more hours today when its center will be over water, and the storm's heavy rains of up to ten inches will cause flash flooding in Mexico's Veracruz state. So far, damage from Ernesto has been modest, with no deaths or injuries reported.


Figure 2. True-color MODIS image from NASA's Terra satellite of Tropical Storm Ernesto, taken at 1 pm EDT August 8, 2012. At the time, Ernesto had top winds of 50 mph. Image credit: NASA.

I'll have a new post this afternoon to talk about July 2012--the warmest month in U.S. history.

Jeff Masters