The tropics continue to remain active in both the Atlantic and Pacific. Tropical Depression Four formed yesterday in the Atlantic, but is likely to be downgraded to a remnant low soon, possibly even this evening. In the East Pacific, Invest 95E has a high chance of developing into a tropical cyclone during the next 48 hours. Looking ahead, both the GFS and some ECMWF runs have indicated the possibility of yet another African tropical wave to develop east of the Lesser Antilles in about 7-10 days.

Tropical Depression Four may no longer even be a tropical cyclone

Tropical Depression Four in the Atlantic has lost organization today, and is on the verge of degenerating into a remnant low. It is unclear at this point if Four even has a well-defined circulation, as noted in the 5:00 p.m. EDT NHC discussion. An ASCAT pass from around 12:00 UTC this morning showed that the circulation had become elongated and lost definition. Since that time, deep convection associated with the depression has greatly diminished today as a result of Saharan Air Layer to the east becoming entrained in the circulation, although some new convection has begun to develop north of the center this evening. Saharan Air Layer outbreaks are normal in July, and they typically limit July development in the Atlantic Main Development Region (MDR).

As of 5:00 p.m. EDT Thursday, Tropical Depression Four was centered near 13.1°N 44.9°W and was moving westward at the fast clip of 23 mph. Maximum sustained winds were estimated at 25 knots (30 mph) with an estimated minimum pressure of 1009 mb. However, the 00:00 UTC ATCF best track indicates that Four’s pressure has risen to 1011 mb. Four is not likely to strengthen, especially since it is in a dry environment and wind shear is expected to increase tomorrow. It seems very unlikely the depression will be able to strengthen into Tropical Storm Don. The NHC expects Four to degenerate into a remnant low by tomorrow, although it is possible it could be declared a remnant low as soon as tonight. As a remnant low, Four is expected to pass northeast of the Lesser Antilles this weekend, before eventually dissipating east of the Bahamas. There is a slight chance that Four could encounter more favorable conditions near the Bahamas, and regeneration cannot be ruled out. The most likely scenario is what is left of Four will not be able to survive the dry air and wind shear, and regeneration will not occur.

Invest 95E in East Pacific likely to become Tropical Storm Eugene this weekend, could become a hurricane

Invest 95E continues to get better organized in the East Pacific, and is likely to become Tropical Storm Eugene by Saturday. The National Hurricane Center (NHC) gives 95E an 80 percent chance of development within 48 hours and a 90 percent chance within 5 days. Model support for Invest 95E is very strong, with the ECMWF, GFS, CMC and UKMET models all predicting development. The 00:00 UTC Friday run of the SHIPS model predicts very favorable conditions during the next 72 hours, with very light wind shear (less than 10 knots), a fairly moist environment, and sea surface temperatures above 27°C (80.6°F). Some rapid intensification is possible with 95E once it establishes a core. Due to favorable conditions during the next 72 hours, I think it is possible 95E could become a hurricane, although a major hurricane is unlikely. However, by 72 hours, 95E is expected to cross the 26°C (78.8°F) isotherm, in addition to entering a drier environment. Weakening should begin by that time as 95E will be moving over progressively cooler waters.

As of 00:00 UTC Friday, 95E was centered near 11.2°N 108.2°W. Maximum sustained winds were estimated at 25 knots (30 mph) with an estimated minimum pressure of 1008 mb. 95E is expected to move to the northwest over the open Pacific, and is not expected to be a threat to land areas.

Another tropical wave to watch – already?

Several recent GFS and ECMWF runs, as well as GEFS and EPS ensemble members, have indicated the possibility of another tropical wave to develop into a tropical cyclone by mid-July. This wave is expected to emerge off the west African coast on Saturday into the Atlantic Ocean, and is expected to continue on a brisk westward motion at a low latitude. This season so far has had unusually strong tropical waves and early activity in the Main Development Region (MDR), and early activity in this region is strongly positively correlated with above average activity in the Atlantic. We will have to keep watching this wave – although it remains far out for now and the NHC has not mentioned it on their Tropical Weather Outlook.

I will be back tomorrow for another post on Tropical Depression Four (or what’s left of it), Invest 95E, and the next African wave to watch. The next name on the Atlantic naming list is Don, and the next name on the East Pacific naming list is Eugene.