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  • Writer's pictureBryan Norcross


What remains of Hurricane Eta is rapidly redeveloping over the warm Caribbean waters off the coast of Belize. Through the day today, the system will lift to the north and slowly strengthen. The system is quite broad, so it will take time to organize and start spinning faster. In general, the bigger the system, the longer the strengthening process takes.

The atmospheric environment over the developing system will be conducive for a new tropical storm to form. Once again, it would be called Tropical Storm Eta because it formed out of the broad rotation related to the original storm.

The system will lift north, grabbed by a sharp dip in the jet stream moving across the Gulf of Mexico. The flow around that dip will act like a scoop to push the new Eta toward Florida along with gobs of tropical moisture from the Caribbean.

The interaction between the jet stream dip and the tropical storm will be complex, difficult to precisely forecast, and will evolve over the next several days. But it’s clear that the flow from south to north over the storm will stretch the moisture toward the Florida peninsula. As a result, that dense tropical moisture will already cover South Florida while the new version of Eta is near or over the Cayman Islands and Cuba.

This means that we can’t look at the cone, and the dots in the middle of it, to forecast where the bad weather will be. The cone tracks the center of the circulation, which is much less relevant in a situation where the storm is interacting with the jet stream. In this case, imagine a large plume of moisture extending north from Eta’s center.

The National Weather Service has issued a Flood Watch for metropolitan South Florida – 6 to 10 inches of rain are forecast over the next several days. It will come in bands, so it’s impossible to know exactly where the heaviest rain will fall. The fact that the ground is saturated will aggravate the flooding problem.

In addition, it will be windy along the entire southeast coastline of Florida. The wind earlier this week was caused by the contrast in pressure between a fairly strong high-pressure system stretched over the western Atlantic to the north and Eta to the south. The bigger the contrast, the stronger our wind.

As the new version of Eta strengthens, the storm's pressure will drop, so the contrast will once again increase. That means the winds will pick up all along the southern Florida coast and in the Keys.

Assuming the center of Eta tracks something like what the National Hurricane Center is forecasting – through the Straits of Florida and near or over the Keys plus or minus – the Keys will be closer to the center and will get additional wind from the circulation itself. Under the currently envisioned scenario, the wind on the east coast of Florida would be mostly from the pressure difference north to south, but it will be quite gusty for 2 or 3 days.

Whenever we have a system coming out of the Caribbean, we are concerned that it might turn into a powerful hurricane, of course. Currently, the National Hurricane Center is forecasting the new Eta to top out as a 65-mph tropical storm.

It’s not out of the realm of possibility that it could get a little stronger, possibly reaching hurricane strength, but the atmospheric environment will be dominated by the jet stream dip, and that should limit the top end of the storm. Some dry air will also be pulled into the circulation, which should also help keep it from getting too strong. There is also a possibility that the winds will stay weaker than forecast.

Remember, intensity forecasts have fairly large intrinsic errors. So when you see 65 mph in a forecast at 4 or 5 days out, add and subtract about 15 mph to understand the average range of wind speeds possible.

To boil this down, in South Florida, a several-day stretch of windy and rainy weather is forecast to start late today. Periods of heavy rain and gusty wind are expected with the wind peaking Sunday and Monday on the current schedule, which is still subject to adjustment. How quickly the rainy stretch will end next week is an open question since the storm is most likely to end up in the Gulf, which means it will continue to pull tropical moisture over the peninsula. The wind, however, should be decreasing noticeably by Tuesday.

In the Keys, closer to the center of circulation, the winds will likely be higher with bands of heavy rain likely. Wind gusts are currently forecast to reach hurricane strength late Sunday and early Monday, plus or minus. Although the worst weather is likely to be in a band to the east of the center of circulation.

Common sense preparations should be made to prepare anything exposed to a strong southeast wind – marine interests beware. Bring in things that could blow around. Park cars on high ground because flooding rain is likely in spots.

It’s important that everybody stay in touch with the latest forecasts. This new Eta has only begun to form, so the details of the forecast may very well change once a new center of circulation clearly develops, which is expected later today or tomorrow.

The video coming out of Central America shows torrents of water rushing downhill through towns. There is no reason the think that anything but a mega disaster occurred there.

Residents in the Cayman Islands should also stay in close touch with local forecasts. Eta’s center of circulation will pass near the islands, although, once again, the worst weather will likely be somewhat displaced from the track of the center of the storm.

Everybody stay informed. The storm is only now in its developing stage.


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