Tropical Activity Ramping Up

Starting August 1st tropical activity begins to ramp up as more disturbances exit Africa and make their way towards the US, wind shear in the tropical Atlantic (which can tear up tropical systems) drops to their lowest levels, vertical instability rises to its highest (better chances for thunderstorms) and sea surface temperatures rise towards their warmest temperatures during the year on average. With that in mind, we have already seen 5 named storms in the Atlantic Ocean with Hurricane Alex actually occurring in January (which is quite rare) and being the strongest storm to have completely dissipated so far with an ACE around 3.6. ACE is a measure of accumulated energy during the tropical system’s life time.  The fifth storm, named Earl just dissipated over the mountains of Mexico. It’s current ACE of 4.1 surpasses Alex’s ACE. The current total ACE is around 9 to 10, which is right around average and matches the average for the year. For what it’s worth the hurricane seasonal forecast is right around average for a typical tropical period.

Hurricane season climatology for number of storms. Peak occurs in September.
Hurricane season climatology for number of storms. Peak occurs in September.
Hurricane Alex's storm track from January. January tropical systems are quite rare because temperatures are quite cool normally.
Hurricane Alex’s storm track from January. January tropical systems are quite rare because temperatures are quite cool normally. Via wunderground.com

 

As we move continue into August, the National Hurricane Center is watching two areas of interest. One is an area associated with a stalled out piece of energy over the Southeastern US/Florida. It’s currently over warmer than normal waters in the Gulf of Mexico, which will help to sustain and possible strengthen it during the next 5 days. Either way, forecast models are putting out some high precipitation totals and flash flooding is very possible during its life time in the area. Another area of interest is being watched in the Western Atlantic just north of Puerto Rico. It is currently being steered by an area of high pressure nearby and, as a result, would curve around it. Sea Surface temperatures are above normal in this area as well, allowing for plenty of energy to sustain it. Shear is nearby the area of interest, but it appears that the shear that is in the storm’s immediate vicinity would be rather low. Both of these storms have a possibility of generating tropical characteristics over the next 5 days, but the one in the Southeastern US/Florida area has the best chance at this time.

Areas worth watching for tropical development in the world based on the ECMWF FOrecast. Notice the recurcing track in the Western Pacific and the probabilities nearby the United States.
Areas worth watching for tropical development in the world based on the ECMWF Forecast. Notice the recurving track in the Western Pacific and the probabilities nearby the United States. Via Allen Brammer.
Areas of interest in the Eastern Pacific over the next 5 days.
Areas of interest in the Eastern Pacific over the next 5 days.
Areas of interest of the next 5 days in the tropical Atlantic.
Areas of interest of the next 5 days in the tropical Atlantic.

 

In the Eastern Pacific, another area of interest has a higher chance for generating tropical characteristics. It is expected to move toward the northwest while combining with remnants of tropical depression Earl. It is over above normally warm sea surface temperatures, but would also be interacting with some shear. This area of instability is worth watching because it is remaining around land and its resulting precipitation and wind field may impact the Central America and southwestern portions of the United States.

Forecasts for 10 to 15 days out based on Rossby waves (top) and analogs (bottom) showing potential for cooler temperatures in the East and Central US. Via Josh Herman (top) and Al Marinaro (bottom).
Forecasts for 10 to 15 days out based on Rossby waves (top) and analogs (bottom) showing potential for cooler temperatures in the East and Central US. Via Josh Herman (top) and Al Marinaro (bottom).

 

Finally, one storm in the Western Pacific, Omais, may impact the United States, not with its immediate effects like wind or precipitation since it’s so far away, but with the fact that it alters our pattern. Often when a storm takes a recurving track in the Western Pacific, they’re taking a warm/moist air mass into an area of cooler/dry air. As a result cooler/drier air usually gets shoved southeast out of Canada and into the Central or Eastern United States usually about 14 days later. Medium to longer range models/approximations are currently picking up on that.

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