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  • Writer's pictureBryan Norcross


Eta is still quite disorganized. The center of the sloppy circulation appears to be on the edge of a mass of thunderstorms that cover the Cayman Islands south of Cuba. Continuous rain is falling there which is quite heavy at times. The latest satellite measurements show that the winds are still fairly low, but the computer forecast models insist that Eta will organize and develop into a tropical storm as it heads toward Cuba.

It is very possible that a new center will form under the thunderstorms to the northeast of the center, essentially jumping the center forward.

Eta is being pushed north by a sharp dip in the jet stream over the Gulf of Mexico. This diving and scooping jet stream will have multiple effects on the future of Eta.

Besides lifting Eta to the north, the dip is pushing the thunderstorms upwind from the center. It is also temporarily making the atmosphere over the storm’s path conducive for strengthening. In essence, the jet-stream dip is lifting the air, helping the thunderstorms grow, which helps strengthen the circulation.

But as time goes on, the strong winds associated with the dip will drive dry air into Eta’s circulation and further tilt the storm to the north. Both of these effects should have a negative influence on Eta’s strength.

All of this means that the Eta’s top winds are unlikely to suddenly increase – although we do have to recognize that a forecast a couple days ahead has an average error of about 15 mph. It also means that the bad weather will be north of the center, which means the forecast cone is not relevant to where the strongest winds and heaviest rain will be.

If the center tracks over the Middle Keys, for example, the strongest band of rain and wind could be over Dade, Broward, or farther north. And there will be multiple bands of gusty squalls.

The spreading out of Eta’s winds and rain toward the north will coincide with the storm merging with the upper-level system related to the jet-stream dip. Eta’s structure will become some more like a nor’easter – shaped like a comma.

As a result of Eta’s forecast increase in size, the National Hurricane Center issued tropical storm alerts for the possibility of winds over 40 mph over the entire southern half of the Florida Peninsula and the Keys. The Bahamian government issued alerts for the Northwest Bahamas as well.

So, what exactly should we expect? Since the jet stream flow is going to tilt Eta to the north, we can expect bands of rain on the Florida side of the storm, even while it's well to the south. The first band will move over the Keys this morning and lift north over the peninsula as the day goes on. Expect a continuous rain with the band, with embedded downpours with gusty winds coming off the ocean. Tides will be extra high because the wind will be continuously pushing the ocean water onshore.

As Eta’s center comes closer to the Keys and southeast Florida on Sunday, the gustiness of the wind and the intensity of the rain will increase and spread to the north. The rain won’t be continuously heavy, but under one of the bands rotating in off the ocean, a lot of rain could fall since the bands won’t be move very fast. This is expected to last into Monday.

The peak effects from Eta are currently expected late Sunday or on Monday. Again, the strongest winds and heaviest rain are likely to be displaced well to the north of the storm's center shown on the cone graphic.

The National Weather Service has issued a Flood Watch for South Florida. Total rain amounts of 8 to 12 inches are forecast. The problem is, the ground is saturated from the excess rain we’ve had this year.

Since most of the bad weather will be north and east of the center, if the center passes over the Keys, those islands to the left of the track would likely get much less rain and wind.

Eta may transition from being called a tropical storm to a subtropical storm, or it could conceivably jump right to Subtropical Storm Eta when it gets winds of 40 mph or higher. So don’t be surprised if you see that designation. It just means that the strongest winds are not around the center, but are displaced to the north, in this case.

This entanglement of Eta and the upper-level jet-stream dip will cause the system to move slowly when it’s in the vicinity of South Florida, which means we should expect an extended period of the bad weather. Since the expected track keeps much of the Florida peninsula on the north or east side of the storm for at least a few days – where the tropical moisture feed is – the rain and gusty winds may hang around into Tuesday or Wednesday, depending on the eventual track of the center of Eta.

Be aware of where your car is parked – avoid putting in under a big tree. Have flashlights on standby, and be sure everything is charged up in case the power goes out in the gusty winds. Secure the pool furniture, or anything that might blow around outside or on your balcony.

Otherwise, just use common sense. Stay off the road in the heavy rain and beware of local flooding.

And by the way, there’s another area out in the middle of the Atlantic that might become the 29th storm of the year. It will not be a threat to the U.S.


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