• Bryan Norcross

Tropics are suddenly a little interesting today

The National Hurricane Center is taking note of two areas in the tropical Atlantic, which is somewhat unusual for this point in the hurricane season. Tropical Disturbance #1 is a small system approaching the Caribbean islands, while Tropical Disturbance #2 is quite large and has just moved off the coast of Africa.



Tropical Disturbance #1: Somewhat unexpectedly, the small disturbance just east of the eastern Caribbean islands briefly developed a circulation yesterday afternoon. The circulation appears to have dissipated today. In any case, the system still has a short window of time to organize enough to be designated a tropical depression or tropical storm before it reaches the islands tomorrow.


The National Hurricane Center is still giving it a very slight chance of organizing into at least a tropical depression.


Hostile upper-level winds are already in evidence near the disturbance, however, so significant development isn’t likely. In any case, gusty tropical weather will pass over the southeastern Caribbean islands over the next couple of days.


As the disturbance approaches Central America next week, we’ll see if it is enhanced by interaction with broad low pressure in that area. This was the mechanism that eventually led to Tropical Storm Claudette last week, but it’s too far out for any certainty. No two scenarios are ever exactly the same.



Tropical Disturbance #2: A large disturbance just emerged off the coast of Africa. Normally we would wait and see what happens once it moves out over the open ocean, especially with so much Saharan Dust just to the north, relatively cool ocean water ahead, and the calendar still on June. But meteorologists took special note yesterday because one of the computer forecast models suddenly got interested in the system.


The disturbances over Africa were extremely robust last hurricane season, and this season seems to be starting the same way. We watch systems that begin to develop in the east Atlantic very carefully because a high percentage of the strongest, most damaging hurricanes originate from disturbances that traverse that area. But that normally happens later in the hurricane season when the tropical ocean has warmed up.


In the case of Tropical Disturbance #2, the European model picked up on the large disturbance and tracked it all the way across the Atlantic. On the other hand, the American G.F.S. model did not show significant development, and the other models showed much less development than the European, if they showed anything at all.


That was yesterday. Now today, the European doesn’t show any significant development, but the G.F.S. shows a system with modest organization.


All this points to an environment that’s marginally supportive of tropical development – right on the hairy edge. So a strong storm is not expected, even if a circulation is able to organize.


The long-range computer forecast models predict somewhat hostile conditions next week when the system, whatever form it takes, gets closer to the Caribbean.


Note that the large cone-like area drawn on the map by National Hurricane Center forecasters is NOT the equivalent of a typical cone of uncertainty. Somewhere in this zone, in their estimation, is where the system could develop sufficient organization to be designated a tropical depression.


The development area is long like that to reflect the significant uncertainty whether the environment just south of the Saharan-dust plume will allow development.


So the questions are: Is the disturbance strong enough to fight off the Saharan dust and acquire an organized circulation? Or does it move west as a moisture surge, like most system do this time of year?