Tropical Disturbance Moving Through Hispaniola: U.S. Threat Ahead?

August 23,2014



 
A tropical disturbance is pushing its way from the Caribbean into the Atlantic, and it is still being closely monitored for potential development into a tropical depression or tropical storm.
Here's what we now know -- and don't know -- about this potential tropical threat.

Where is the Disturbance Now?

As shown in the infrared satellite image above, the general area of disturbed weather has now pushed north of the Caribbean Sea, affecting portions of Haiti and the Dominican Republic.
Air Force Hurricane Hunters flew into this disturbance Friday afternoon and evening to determine whether a surface low pressure circulation -- which requires that not only the east or northeast winds typically found in the Northern Hemisphere tropics, but also a westerly wind -- be present.
The Hurricane Hunters found a small area of low pressure with a poorly-defined circulation. However, it did find a small area of tropical storm-force winds. While the NHC opted not to initiate advisories, it is possible that Tropical Depression Four -- or, given the wind speeds, Tropical Storm Cristobal -- could be christened within the next 48 hours if the system's convection and circulation can just get a little better organized.
This is the first hurdle for this system to clear.
(MORE: Tropical Terms You Need to Know)

Caribbean Impact

Rain and gusty winds will continue to spread through the Caribbean through the weekend, regardless of what the system is called.
Mudslides and flash flooding have already been reported throughout the island of Puerto Rico on Friday afternoon.
Through the overnight, locally heavy rain will fall over parts of the Virgin Islands, Puerto Rico, Haiti, the Dominican Republic and the Turks and Caicos.
(FORECASTS: St. Thomas | St. Croix | San Juan | Punta Cana)
This weekend, bands of rain will spread into the southeast Bahamas, Jamaica, Cuba and possibly the Cayman Islands.
(FORECASTS: Ocho Rios | Grand Cayman | Nassau)
Local flash flooding is a possibility, particularly over mountainous terrain of Puerto Rico, Haiti, the Dominican Republic, Jamaica and eastern Cuba. Flood watches have been posted for Puerto Rico and the U.S. Virgin Islands.
Again, it remains to be seen whether the system will be Cristobal, a depression or still a fledgling tropical disturbance, which will also, of course, factor into other potential impacts, including winds, coastal flooding and high surf. A track over more land would also limit development of the system in the Caribbean.

U.S. Threat?

To be clear, it is still too soon to determine with certainty if this system will have any direct impacts on the mainland U.S.
(MORE: Why Long-Range Model Forecasts in the Tropics Can't Often Be Trusted)
A crucial player in determining if the U.S. will be impacted appears to be a southward dip in the jet stream expected to carve out over the western Atlantic Ocean. There appear to still be three scenarios at this time:
1) Avoiding the U.S.: If the system tracks farther north in the Caribbean, and the jet stream dip is sufficiently strong and penetrates far enough south, the system may turn sharply north, then northeast after leaving the southeast Bahamas. In this scenario, the U.S. coast would be missed -- except for perhaps some high surf next week.
2) East Coast threat: If the system either isn't pulled far enough north by the jet stream dip or the jet stream dip passes by into the north Atlantic, it may track much closer to at least part of the East Coast next week.
3) Gulf of Mexico:  The system may continue toward the west-northwest, then head into the eastern Gulf of Mexico where it would strengthen. For now, this scenario appears to have a low, but not zero probability.
Forecast uncertainty is typically very high several days out even in cases of a well-defined tropical cyclone, which we don't have yet. Therefore, we cannot take either of these scenarios completely off the table yet.
All interests along the East Coast should closely monitor the progress of this system. Check back with us at The Weather Channel and weather.com for the latest on this potential threat.
(EXPERT ANALYSIS: The Weather Channel | Dr. Jeff Masters from Weather Underground)
In the meantime, now is an excellent time to make sure you're hurricane ready.