Humberto Becomes the Atlantic's First Hurricane of 2013

The Atlantic's first hurricane of 2013 finally arrived this Wednesday morning, as Hurricane Humberto intensified into a minimum-strength Category 1 hurricane in the far Eastern Atlantic. Humberto is listed in NHC's preliminary Best-Track data repository as having achieved hurricane strength at 8 am EDT on September 11, which would tie it with Hurricane Gustav of 2002 for the latest appearance of the season's first hurricane, since 1941. Humberto is also Earth's first tropical cyclone to reach Category 1 strength in three weeks--the last was Typhoon Trami, which hit China on August 21 as a Category 1 storm with 85 mph winds. To go three weeks during late August and early September without a Category 1 or stronger tropical cyclone is a very unusual event. Satellite loops show that Humberto is a small but well-organized hurricane with a prominent eye, located just west of the Cape Verde Islands. Humberto has until Thursday night to continue the intensification process, at which time high wind shear and cooler waters will likely cause weakening. Humberto is not expected to be a threat to any land areas.


Figure 1. First eye of 2013: MODIS satellite image of Hurricane Humberto, taken at 8:30 am EDT on September 11, 2013. At the time, Humberto was a Category 1 hurricane with 75 mph winds. Humberto was declared the Atlantic's first hurricane of 2013 in the 5 am EDT advisory on September 11. Image credit: NASA.

Gabrielle hits Bermuda
Tropical Storm Gabrielle blew past Bermuda last night, bringing sustained winds of 40 mph, gusting to 53 mph, along with just over an inch of rain to the Bermuda Airport. Satellite loops show that high wind shear of 20 - 25 knots has ripped apart Gabrielle, leaving the storm with almost no heavy thunderstorms, exposing the low level circulation to view. Wind shear is expected to remain high for the next two days, which will likely keep Gabrielle from strengthening. On Friday and Saturday, moisture from Gabrielle or its remnants will likely bring heavy rain to the Canadian Maritime Provinces.


Figure 2. Radar image of Tropical Storm Gabrielle at 9:03 pm AST September 10, 2013. At the time, Gabrielle had top winds of 60 mph, and strong upper level winds out of the west had pushed Gabrielle's heaviest thunderstorms to the east side of the center of circulation. The island is under the white "+" at the center of the image. Image credit: Bermuda Weather Service.

93L a threat to develop in the Gulf of Mexico
A trough of low pressure over Mexico's Yucatan Peninsula (Invest 93L) is generating heavy rains over the peninsula and adjacent waters as it moves west-northwest at 5 - 10 mph. Satellite loops and radar loops from Mexico and Belize show that 93L has a decent amount of spin and a modest area of heavy thunderstorms. After 93L emerges over the Southwestern Gulf of Mexico's Bay of Campeche on Thursday, the disturbance has a high chance of developing into a tropical depression as it crosses the Bay of Campeche. The atmosphere will be unusually moist, ocean temperatures will be a very warm 29°C (84°F), and wind shear will be a moderate 10 - 15 knots, according to the latest SHIPS model forecast. The computer models predict a landfall location along the Mexican coast between Veracruz and a location a few hundred miles south of the Texas/Mexico border by early next week, and it appears that 93L's heaviest rains will stay south of Texas. In their 8 am EDT Wednesday Tropical Weather Outlook, NHC gave 2-day odds of development of 40% and 5-day odds of 70%. Due to its slow motion, 93L will have more time to intensify than the other storms we've seen in the Bay of Campeche this year--Tropical Storm Barry, Tropical Storm Fernand, and Tropical Depression Eight--and 93L will likely pack heavier rains and higher winds at landfall than these three previous storms.

Jeff Masters