ETA LIKELY TO REFORM IN THE CARIBBEAN AND AFFECT SOUTH FLORIDA THIS WEEKEND

Eta has weakened into a Tropical Storm as expected. Its center has now moved into the mountainous areas of Nicaragua and Honduras. The high terrain will shred the surface circulation before what’s left of the system drifts back over the Caribbean and into the waters south of Cuba about Friday.

The huge threat now becomes the torrential rain that will fall over the mountains of Central America with 2 to more than 3 feet forecast for Nicaragua and Honduras, and at least 1 to 2 feet predicted in the surrounding countries – Belize, Guatemala, and Costa Rica. Landslides and flash flooding are all but assured over a large area today, tomorrow, and into Friday at least.

By Friday, the remnants of Eta will start to be pulled north over the warm Caribbean waters between Central America and Cuba. At this point the details of the forecast get very complicated, but the basic idea seems clear.

An unusually strong and deep dip in the jet stream will move across the Gulf of Mexico, scoop up the system, and fairly quickly lift it and a mass of tropical moisture north toward South Florida.

The surge of moisture over the Florida peninsula will begin tomorrow when the cold front that came though on Monday gets pulled back north. The combination of the strong wind off the ocean, the old front, and the tropical moisture is expected to begin a period of heavy rain over the southern peninsula – which will fall on top of already saturated ground.

In the meantime, the remnants of Eta are forecast to be moving over the Caribbean waters by Friday. It is likely that Eta’s surface circulation will have been destroyed by the mountains, so the system that tracks to the north will have to reorganize a circulation using the surviving upper-level part of Eta as a starting point. Assuming a new tropical system develops as expected on Friday or Saturday, it might be called Theta – the next letter in the Greek alphabet.

Technically, a system has to maintain its surface circulation to keep the same name if it regenerates. The National Hurricane Center will make the call. For now, they are using one cone to convey the forecast for clarity, though in the end, it might be determined that Eta ended over the mountains of Central America and Theta formed in the Caribbean. The naming details aren’t important to the weather, obviously.

The bottom line is that a combination of two systems – the strong upper-air disturbance in the form of the sharp jet-stream dip and the tropical system from the Caribbean – are forecast to move in the direction of South Florida, either of which would produce heavy rain on its own. How exactly they will interact is impossible to say, but a period of gusty wind and heavy rain over the weekend is likely. The question is only a matter of degree.

The upper-level weather pattern that the jet-stream dip is likely to create should initially be conducive for Eta/Theta to organize and intensify, at least a bit. As the upper system and the tropical system come together near Florida, however, the systems will interact in difficult-to-predict ways.

It’s likely that the bulk of the rain and the wind will be shoved to the north and east side of Eta/Theta/whatever. It’s also likely that the track of the tropical system will arc back to the west and then maybe back to the east in some kind of S-curve. Though the details are foggy.

The interaction of the two systems should keep Eta/Theta from getting too terribly strong. The National Hurricane Center is forecasting a healthy tropical storm when the system is close to South Florida at the current time, although we all know that intensity forecasts for systems that haven’t even yet developed are iffy at best.

Still, as a general statement, it doesn’t appear that the forecast atmospheric pattern would support a super-strong storm.

The boil it down, the period of rainy and windy weather in South Florida is expected to begin in the second half of tomorrow with the moisture increasing from south to north. The wind and rain may increase over the weekend as Eta/Theta moves into the picture, though the farther in the future we try to predict, the fuzzier things get.

On the current schedule, the effect of Eta/Theta would peak on Sunday or Monday, but last into next week. As the system tracks to the north, it might continue to drag tropical moisture over the Florida peninsula.

For now, prepare for an extended period of heavy rain, and have your hurricane supplies in place in case you get stranded by local flooding and/or power outages. Gusty winds with saturated ground can lead to trees coming down on power lines.

We’ll just have to see how this complex scenario develops. Be ready for changes in the details of the forecast.