As one-time hurricane Gordon and one-time tropical storm Helene move out of the picture, three other disturbances are brewing in the tropical Atlantic.
Let’s begin examining the disturbance known as AL94. Of the active systems, it has the greatest potential to impact the U.S. but its future course and development remain highly uncertain.
AL94 - Isaac???
This disturbance has been trekking westward across the deep tropics since it left the African coast on August 16. It still has not reached the tropical depression stage, and this morning’s satellite presentation is less than impressive. However, it could intensify into a tropical storm in the next couple days, earning the name Isaac.
The path it takes to get there takes it over Hispaniola, then between Cuba and the Bahamas where it picks up in intensity. Of course, models that far out aren’t very reliable, and shift around a bit with each run, but it’s wise to be aware of the possibilities.
Rather than focusing on a single run from a single model, it is common practice to assemble output from various models, and ensembles of those models, monitor their trends and biases, then make a forecast from that information. In the 5-7 day period and beyond, weather details become fairly unpredictable, and with hurricanes, their track affects the intensity, and their intensity affects the track, making it especially complicated.
Over the weekend, Gordon, which began as an easterly wave off the coast of Africa on August 9th, was first declared a tropical depression on August 15, then a tropical storm on August 16, and then a hurricane on the 18th. Gordon was the third hurricane of the Atlantic season, after Chris and Ernesto.
Helene and AL95
On Friday evening, the remnants of tropical depression 7 were revived after spending six days as an open wave. Aircraft reconnaissance flights into the disturbance in the southwestern Gulf of Mexico found 45mph winds and a 29.65“ (1004mb) central pressure, so it was upgraded to tropical storm helene.
The third disturbance in the Atlantic is an easterly wave that exited the African coast on Saturday. It’s centered a couple hundred miles south of the Cape Verde islands and is still in the formative stage. This is no threat to land any time in the near future, and may not be too quick to develop either.
Climatologically, we only get to the 9th name on the list on October 4, so if Isaac forms this week, we are way ahead of an average season. As far as hurricanes go, we’ve had 3 so far, and during an average season, the third occurs on September 9.
On the graph below, the climatological seasonal cycle of tropical storms and hurricanes (red) and hurricanes-only (yellow) is shown, with today’s date marked by the vertical green line. You can clearly see that we are just getting into the heart of hurricane season now, and the abundance of activity in the basin normally occurs between about August 20 and October 20.
The author, Brian McNoldy, is a senior tropical weather researcher at the University of Miami/Rosenstiel School of Marine and Atmospheric Science. He is a new tropical weather blogger for the Capital Weather Gang.