Tropical Storm Humberto Drenching the Cape Verde Islands

Tropical Storm Humberto, the eighth named storm of the 2013 Atlantic hurricane season, is here. Humberto has formed unusually far to the east, between the coast of Africa and the Cape Verde Islands. Tropical Storm Warnings are flying in the southern Cape Verde Islands, and Humberto's rain bands have already arrived in capital city of Praia, where 1.46" of rain has fallen, with sustained winds as high as 26 mph. Humberto's west to west-northwest motion at 12 mph will keep the storm just south and west of the islands through Tuesday, but this path will be close enough to bring potentially dangerous rainfall amounts of 3 - 6 inches to the southern islands. Satellite loops show that Humberto is well-organized with plenty of spin and a growing amount of heavy thunderstorms. The models are bullish of developing Humberto into a hurricane just west of the Cape Verde Islands by Wednesday. If Humberto reaches hurricane strength before 8 am EDT on Wednesday, 2013 will avoid setting the record for the latest formation date of the Atlantic's first hurricane, dating back the beginning of the aircraft reconnaissance era in 1944. Humberto is expected to take a sharp northwards turn later this week, which will carry the storm into a region of ocean where no land areas would likely be at risk from a strike, with the possible exception of the Azores Islands.


Figure 1. Morning satellite image of Tropical Storm Humberto, taken at 7:45 am EDT September 9, 2013. Image credit: NOAA.

Cape Verde Islands Hurricane History
The Atlantic's most terrifying and destructive hurricanes typically start as tropical waves that move off the coast of Africa and pass near the Cape Verde Islands. This class of storms is referred to as "Cape Verde hurricanes", in reference to their origin. Despite the fact that the Atlantic's most feared type of hurricanes are named after the Cape Verde Islands, these islands rarely receive significant impacts from one of their namesake storms. This is because tropical waves coming off the coast of Africa have very little time to organize into tropical storms before arriving at the Cape Verde Islands, which lie just 350 miles west of the African coast. According to EM-DAT, the International Disaster Database, there have been only two deadly tropical cyclones in Cape Verde history. The deadliest was Tropical Storm Fran of 1984, which brushed the southwestern islands on September 16 as a tropical storm with 50 mph winds. Fran brought sustained winds of 35 mph and torrential rains to the islands. The rains triggered flash flooding that killed 29 - 31 people and caused damages of almost $3 million (1984 dollars.) The other deadly named storm was Tropical Storm Beryl of 1982, which passed about 30 miles south of the southwestern islands on August 29, with 45 mph winds. The storm's heavy rains killed three people on Brava Island, injured 122, and caused $3 million in damage.

The most recent named storm to affect the islands was Hurricane Julia of 2010, which was the easternmost Category 4 hurricane ever recorded in the Atlantic. Julia passed about 50 miles south of Sao Filipe in the southern Cape Verde Islands as a tropical storm with 45 mph winds, bringing wind gusts of 30 mph to the islands and some minor flooding.


Figure 2. Track of Tropical Storm Fran of 1984, which brushed the southwestern Cape Verde Islands on September 16 as a tropical storm with 50 mph winds. Torrential rains from Fran killed 29 - 31 people in the Cape Verde Islands, making it the deadliest storm in their history.

Ex-Gabrielle
The remnants of Gabrielle (now being called Invest 92L) are generating heavy thunderstorms about 500 miles south-southwest of Bermuda, as seen on satellite loops. High wind shear of 25 knots is inhibiting development, and wind shear is expected to stay high for the next three days. The disturbance is headed to the north-northeast to northeast at 10 mph, and is expected to pass several hundred miles east of Bermuda Tuesday through Wednesday. Since strong westerly winds are keeping most of ex-Gabrielle's heavy thunderstorms displaced to the east, the bulk of this activity should miss Bermuda. NHC put ex-Gabrielle's 2-day and 5-day odds of development at 20% in their 8 am EDT Monday Tropical Weather Outlook.

Jeff Masters