Dry Air Dominating the Tropical Atlantic; the Pacific Quieting Down

Tropical wave 94L was located near 14°N, 35°W on Tuesday morning, but is no longer a threat to develop. Satellite loops show that the wave has lost nearly all of its heavy thunderstorms, and water vapor satellite images and the Saharan Air Layer analysis show that 94L is now embedded in a very dry environment. The wave should arrive in the Lesser Antilles Islands on Saturday, bringing gusty winds and heavy rain showers. None of the reliable computer models for predicting tropical storm formation (the GFS, European, and UKMET) develop 94L or anything else in the Atlantic during the coming five days. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave 94L a 0% chance of developing. Like last year, the tropical Atlantic and Caribbean continue to be dominated by high pressure and dry, sinking air, which discourages tropical storm formation. The latest 2-week run of the GFS model shows this pattern continuing into at least the last week of August.


Figure 1. Satellite analysis of the Saharan Air Layer (SAL) done at 8 am EDT August 12, 2014, shows a large area of dry air covering much of the Atlantic. The dry air comes from both the Sahara and from sinking air from an unusually strong area of high pressure over the Atlantic. Image credit: University of Wisconsin CIMSS/NOAA Hurricane Research Division.


Figure 2. Vertical instability over the tropical Atlantic between the Lesser Antilles Islands and coast of Africa in 2014. The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Normal instability is the black line, and this year's instability levels are in blue. The atmosphere has been dominated by high pressure and dry, sinking air since February, which has made it difficult for tropical storms to develop. Instability has also been unusually low over the Caribbean, but has been near average over the rest of the Atlantic. Image credit: NOAA/CIRA.

The Pacific quiets down
In the Pacific, we have only one active named storm: Tropical Storm Julio, with top winds of 65 mph, which is about 700 miles north of Hawaii and headed northwards out to sea. Julio passed well north of the Hawaiian islands over the weekend, maintaining hurricane strength over a portion of the ocean where no hurricane had ever been recorded before.

NHC is tracking two disturbances in the Eastern Pacific: Invest 99E, located a few hundred miles south-southwest of Manzanillo, Mexico, and an area of disturbed weather located about 1500 miles east-southeast of the Big Island of Hawaii. Residents of Hawaii should keep an eye on this second disturbance, which NHC gave 2-day and 5-day odds of development of 10% and 30%, respectively, in their 8 am EDT Tuesday Tropical Weather Outlook. The GFS model predicts this disturbance will develop by this weekend and come within 500 miles of Hawaii in 7 - 8 days. The model also predicts that 99E will develop, but stay well away from any land areas.


Figure 3. Enormous tree damage was done to forests on Hawaii's Big Island by Tropical Storm Iselle. Image credit: wunderphotographer mountainwx.

Hawaii cleans up after Tropical Storm Iselle
Power is still out to about 10% of the people on Hawaii's Big Island from Tropical Storm Iselle, which hit the southeast shore of the island on Friday as a tropical storm with 60 mph winds. Iselle is only the second tropical storm on record to hit the Big Island, and was the strongest. About 22,000 customers lost power during the height of the storm on the Big Island, and many of the 8,000 customers still without power may not see their electricity restored until next week, said Hawaii Electric Light. The power company said, "the extent of damage is worse than anything we’ve ever seen here." Iselle damaged about 150 homes and businesses on the Big Island.

Jeff Masters