A Rare Tropical Cyclone-Free September 8th for Earth

It's a rare tropical cyclone-free September 8th on Earth, without a tropical depression, tropical storm, hurricane, or typhoon in the Atlantic, Pacific, or Indian Oceans. Considering that the first two weeks of September are the peak of the tropical cyclone season in the Atlantic, Eastern Pacific, and Northwest Pacific, today's lack of activity is quite unusual. It looks like the Atlantic will be the ocean basin to break the tropical cyclone-free spell, as a strong tropical wave (Invest 91L) emerged from the coast of Africa on Saturday, and is now moving west-northwest at 10 mph towards the Cape Verde Islands. Satellite loops show that 91L is well-organized with plenty of spin and a growing amount of heavy thunderstorms. All of the models develop this wave into a tropical depression just west of the Cape Verde Islands by Wednesday, and 91L has the potential to intensify into a hurricane by late in the week. The storm is expected to track to the northwest into a region of ocean where the Azores Islands would likely be the only land area at risk from a strike. In their 8 am EDT Sunday Tropical Weather Outlook, NHC put the 2-day odds of development at 70%, and the 5-day odds at 90%.


Figure 1. Could this be the beginnings of the Atlantic's first hurricane of 2013? MODIS satellite image of tropical wave 91L off the coast of Africa, taken at approximately 8 am EDT September 8, 2013. All of the models develop this wave into a tropical depression by Wednesday, and some of the models show it growing to hurricane strength by the end of the week. Image credit: NASA.

Ex-Gabrielle
The remnants of Gabrielle (now being called Invest 92L) are generating heavy thunderstorms about 400 miles north of the Eastern Dominican Republic, as seen on satellite loops. High wind shear of 20 knots is inhibiting development, and wind shear is expected to stay high for the next five days. NHC put ex-Gabrielle's 2-day odds of development at 10% and 5-day odds at 30% in their 8 am EDT Sunday Tropical Weather Outlook. The disturbance is headed to the northeast at 10 mph, and is expected to pass several hundred miles east of Bermuda on Tuesday.

Jeff Masters