Subtropical Storm Ernesto over the Northern Atlantic and Tropical Storm Lane over the eastern Pacific have both intensified since yesterday. Ernesto is likely to become a post-tropical cyclone on Friday, while Lane is likely to continue to strengthen and become a major hurricane as it enters the Central Pacific. In the tropical Atlantic, a tropical wave, Invest 99L, has a low chance to develop into a weak tropical cyclone as it approaches the Windward Islands this weekend.

Ernesto slightly stronger but expected to become post-tropical on Friday

As of 11:00 a.m. EDT Thursday, Subtropical Storm Ernesto was centered near 42.0°N 43.2°W, and was moving northeastward at about 16 mph. Maximum sustained winds were 40 knots (45 mph), with an estimated minimum pressure of 1007 mb. Ernesto remains a subtropical cyclone, since the cyclone still has a large radius of maximum winds and the deep convection remains somewhat fragmented. Although some slight additional strengthening cannot be ruled out, Ernesto has most likely reached its peak intensity, and should become a post-tropical cyclone by Friday morning. It is interesting to note that the 18z best track has classified Ernesto as a fully tropical storm, and Ernesto should be upgraded to a tropical storm in the next advisory. Despite low wind shear, Ernesto is already beginning to move over sea surface temperatures below 25°C (77°F). After merging with a frontal zone late Saturday, Ernesto’s extratropical remnants may bring heavy rainfall and strong winds to the British Isles.

Lane gradually strengthening over the eastern Pacific, likely to become a hurricane by tomorrow

As of 8:00 a.m. PDT (11:00 a.m. EDT), Tropical Storm Lane was centered near 10.6°N 127.6°W, and was moving westward at about 14 mph. Maximum sustained winds were 50 knots (60 mph), with an estimated minimum pressure of 1001 mb. Lane is gradually getting better organized, though the cyclone still lacks a well-defined inner core. Once an inner core develops, more steady to perhaps rapid intensification will likely begin. Lane should become a hurricane early tomorrow morning, and will likely become a major hurricane by Sunday. For the next four days or so, environmental conditions are expected to be quite favorable for intensification, with wind shear less than 10 knots and sea surface temperatures around 27-28°C (80.6-82.4°F). By early next week, the wind shear could increase somewhat, which should cause Lane to weaken shortly after entering the Central Pacific basin. Although the majority of the model guidance predicts that Lane will remain south of the Hawaiian Islands, it is too early to rule out impacts to the island chain.

99L only has a low chance to develop, potentially another eastern Pacific system next week

As is typical for mid-August, we begin looking at tropical waves in the deep Atlantic tropics for possible tropical development. Invest 99L, one of the most impressive tropical waves so far in 2018, is currently being monitored for potential development as it approaches the Windward Islands. As of 18:00 UTC Thursday, Invest 99L was located near 10.0°N 50.6°W, and was moving westward at about 15 mph. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1013 mb. The National Hurricane Center (NHC) currently gives 99L a 20 percent chance of development, both within 48 hours and five days. Although environmental conditions are expected to be fairly conducive for development for the next few days (wind shear in the light to moderate range of 10-20 knots and sea surface temperatures above 28°C/82.4°F), the reliable global models show little to no development of this wave. This could be due to the weak surface reflection with the wave, or the wave’s fast movement. The 12z Thursday GFS, ECMWF, and UKMET models are in good agreement that 99L will only be a strong tropical wave as it approaches the Windward Islands. The showers and thunderstorms associated with 99L remain disorganized, and there is currently no signs of a surface circulation trying to develop. As 99L enters the eastern Caribbean, environmental conditions will become hostile for development, and no development is anticipated after that time. However, it should be stressed that we are entering the climatologically active part of the hurricane season, and these tropical waves must be watched closely. If 99L develops into a tropical storm, it would be named Florence.

In the eastern Pacific, a new area of low pressure could form well southwest of the Baja California Peninsula during the next few days. This system could gradually develop into a tropical cyclone as it moves westward to west-northwestward. The NHC currently gives this system a near zero percent chance of development within 48 hours, and a 20 percent chance within five days. The next name on the eastern Pacific naming list is Miriam.

I will be back with an update on the tropics tomorrow.