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Surprising developments in Caribbean — a system to watch

A satellite view of the tropics on Oct. 23, 2020.
A satellite view of the tropics on Oct. 23, 2020.

The broad tropical disturbance that was partially responsible for the extended stretch of wet weather over South Florida is now organizing near the Cayman Islands south of Cuba. A bubble of conducive atmospheric conditions has moved over the system giving it the opportunity to develop a circulation.

Bands of rain associated with the broad circulation are still rotating in the direction of South Florida, but they are farther apart and not as strong since the other factors involved in the heavy rain episode have moved out of the picture. Still, some tropical downpours are expected where one of these bands comes ashore.

Yesterday, the thinking was that a dip in the jet stream across the southern states would come along and scoop the disturbance and its moisture to the northeast across the Bahamas. The moisture, in that scenario, would brush South Florida over the weekend.

We mentioned that the systems were subtle, and the forecast was iffy. Well, now the scenario is different.

The weak jet stream dip is still forecast to come along, but instead of scooping the system to the north, it now appears that only moisture will be pulled out of the system and streamed in the direction of South Florida and the Bahamas over the next couple of days. The center of the circulation is now forecast to stay south of Cuba over the weekend.

To what extent the moisture plume will cover South Florida tomorrow and Sunday is an open question.  A slight deviation in the flow from the jet stream dip could direct the bulk of the moisture just offshore with most of it in the Bahamas.

We need to be ready for the possibility of heavy rain over the weekend across South Florida and the Keys, and be happy for the bonus sunshine if the moisture plume stays just offshore.

After the weekend, the consensus of the computer forecast models is that the Caribbean disturbance will move north into the Gulf of Mexico.

The National Hurricane Center is giving the disturbance a decent chance of developing into at least a tropical depression over the next few days. It could even do that fairly soon while it’s still in the Caribbean.  The depression designation comes when the circulation is defined and supporting thunderstorm development.

There is no good consensus for what shape the system will be in next week. Some long-range computer forecast models track it north in the Gulf as an organized system, possibly Tropical Storm Zeta, while others forecast it to die out.

Whatever happens in the long term, however, it appears that the Florida peninsula will be on the wet side of the system as it continues to pull tropical moisture overhead for the next few days at least.

These quick changes in the forecast are a reminder that weak and developing systems are almost always poorly forecasts. So be ready for more changes as things develop.

Out in the Atlantic, Hurricane Epsilon is now well past Bermuda heading into the North Atlantic’s hurricane graveyard.

Once we’re past this Caribbean disturbance, the long-range computer forecast models indicate that dry air will push in. Hopefully, that will be the season change we’ve been waiting for.

Advisory summary for Hurricane Epsilon
Advisory summary for Hurricane Epsilon

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