Tropical Disturbance #1 is a cluster of disturbed weather approaching the halfway point between Africa and the Caribbean. It’s raising eyebrows because computer forecast models show it developing into a significant tropical system – possibly a hurricane – near or east of the Bahamas next week.
Right now, the system is embedded in a larger area of showers and thunderstorms, so computer forecasts would have to be lucky to accurately predict exactly where an organized system might form from the broad disturbance. But we are moving toward the peak of hurricane season, so it’s appropriate to pay attention.
The National Hurricane Center is giving the disturbance a high-medium chance of developing into at least a depression next week, and those odds will increase if the current trends in the computer forecasts continue.
Saharan dust and dry air continue to dominate the tropical Atlantic, which should slow down development of a depression or storm. But if the computer forecasts are correct, it will arrive near the northeast Caribbean around Tuesday and be in the vicinity of Puerto Rico or the nearby islands midweek.
We are talking about five days from now, so just based on how far that is in the future, the forecast has significant uncertainty. And in this case, the system hasn’t even begun to develop, which adds iffiness to any specific predictions. But currently, the consensus is that the system would not have time to get terribly strong when it reaches the islands.
Still, everybody in the northeast Caribbean should stay up to date on the forecast, which is subject to change. The system could be intensifying about the time it reaches the vicinity of Puerto Rico and the surrounding islands, which are past the dense part of the Saharan dust.
A pronounced dip in the jet stream is forecast to lodge over the eastern U.S. towards the end of next week, which, according to the consensus of the computer forecast models, will pull the system north. But the various computer forecasts do not agree on the orientation and location of the jet stream dip or dips, so there’s no consensus prediction how sharp the turn north will be.
The bottom line is that we will have to watch developments closely next week. Stay tuned.
Debby has ended its run as a tropical system. It has merged with a cold front moving toward the East Coast. The dip in the jet stream that is pushing the front along is spreading Debby’s moisture north. Significant flooding is possible from the Carolinas to Canada. The highest risk is well inland from the northern tip of Virginia across Pennsylvania and Upstate New York.
By midday Saturday, the front will clear the East Coast and push the moisture out to sea.
Flooding will continue in the Carolinas, however, because water that fell in the South Carolina Midlands or the North Carolina Piedmont still has to flow downhill to the Atlantic Ocean. Everyone in the Lowcountry of South Carolina and the lower elevations in North Carolina near a river, creek, or stream should pay attention to local information and instructions. Dangerous conditions will persist for days in some areas.
The overall atmospheric pattern is becoming increasingly conducive to tropical development. The pulse that moves around the Earth called the MJO is moving into a position that is extra supportive of thunderstorms over the Atlantic, which are necessary for tropical storms to develop into hurricanes.
Thankfully, the Saharan dust is hanging on. Normally, dust season ends in the middle of August, but sometimes it continues for a while longer. We can hope that will happen, but the dust only affects the tropical Atlantic east of the islands. The Caribbean and the rest of the Atlantic are still extra warm and mostly dust-free. There is plenty of room for tropical systems to develop.
It’s that time of year. We have to pay attention.
Original article source: Bryan Norcross: As Debby heads north there is another system to watch in the Atlantic
Source Agencies
