93L (finally!) showing signs of development

June 24, 2010

One of the recurring themes inferred from this week’s Tropical Weather Outlooks was the lack of a defined circulation associated with Invest 93L, therefore any development would occur later rather than sooner. This afternoon, however, a low level circulation became apparent, and “later” has become “now” or “real soon”.    The latest TWO from the National Hurricane Center forecasts a 60% chance of tropical cyclone formation in the next 48 hours.

For most of the past week, the NHC has been tracking a notional “center” of activity, along the axis of the tropical wave 93L was associated with.  The Satellite Analysis Branch of NOAA, which provides position estimates based on satellite imagery, which is part of the data NHC uses in its tracking, followed a very different notional center,  which tended to be in the areas of thunderstorm activity well to the west of the wave axis.  This afternoon, the two sets of position estimates came much closer together due to visual satellite imagery showing showing the hint of a low level circulation.  Still shots don’t really due it justice, but here is one anyhow, with the apparent surface circulation circled.

University of Wisconsin’s shear analysis as well as GFS model analysis fed to SHIPS, shows a very favorable environment with less than 10 knots of shear.  The Tropical Cyclone Heat Potential chart shows a quite favorable situation as well. The only near-term potential downside I see is shown in this wider view of the Carribean:

There’s quite a bit of thunderstorm activity that is not directly associated with the surface circulation.  Watching this picture in motion, I am reminded of Pacific storms in the embryonic state, where it takes 24-72 hours for this activity to become focused into one coherent system.  If that sort of situation occurs with 93L, it won’t have much time develop before crossing the Yucatan peninsula.

Using hurricane historical tracks, I made an image of June tropical depressions that formed in the area immediately east of Honduras and the Yucatan.

Based on current motion, the climatological signal (albeit based on few cases) is for a developing storm to stay clear of the central Gulf of Mexico. The most recent run of the ECMWF model shows a repeat of the 1920’s storms. However, at the moment, most other dynamic model guidance (that shows a developing storm) portrays the system  recurving in the Gulf, and heading to Louisiana/Mississippi on a northeast trajectory.

For the past two days, Hurricane Hunter flights have been tentatively scheduled (a day in advance) only to be canceled in the morning. A mission is scheduled for tomorrow, launching at 10:30 AM to arrive in the storm area by 2:00 PM.  Given current trends, it is highly likely that flight will actually take place.

Provided that my Internet Service Provider does not revert to using IP over avian carriers as it seemed to this morning, I’ll post an update around 6:30 AM (EDT) tomorrow, with maybe a quick note or two on Friendfeed during the day.

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