Tropical Storm Erika has formed east of the Leeward Islands

An Air Force Reconnaissance mission has determined that the vigorous tropical wave that was being monitored during the last few days has developed a closed-circulation and winds in excess of 40 mph, it is therefore classified as Tropical Storm Erika. The initial forecast from the National Hurricane Center projects Erika to pass north of the Antilles and the Bahamas as it moves on a generally, northwestward track during the next five days. Tropical Storm Watches have been posted for parts of the Leeward Islands. A complete listing of the watches can be found on the NHC website at http://www.nhc.noaa.gov.

For the intensity forecast, there is a decent amount of uncertainty. The NHC points out that while global models forecast an increase in wind shear (thus weakening Erika), two very reliable models, the GFDL and HWRF, bring Erika to hurricane status despite the wind shear. In my opinion, it is likely that by day five, Erika will be either a strong tropical storm or weak hurricane (winds in the 70 to 80 mph range).

Related to the uncertain intensity forecast, the track forecast is also somewhat uncertain. Should Erika stay relatively weak or weaken during the next few days, she would take a more southern track, posing a stronger threat to the Bahamas and Florida. Should Erika intensify, she would feel the effects of a weakness in a ridge of high pressure to the north and bend more northwesterly this weekend, possibly posing a threat to northern Florida or the southeastern coast of the United States.

Bottom line:

• Tropical Storm Watches in effect for parts of the Leeward Islands.
• Interests in the Virgin Islands, Puerto Rico, Dominican Republic, Haiti, and the Bahamas should monitor the progress of Erika.
• Erika is less likely to impact the United States the stronger she becomes. In other words, a weak storm will stay on a more westerly course and a strong storm would turn more north-northwesterly.
• Large uncertainty in intensity forecast means significant uncertainty in the track forecast.