MIAMI – The news continues to be ominous about Florence. The system is re-organizing and restrengthening. The estimated peak winds are now 70 mph, just below hurricane strength. The hostile upper-level winds are relenting on schedule -- and the storm is heading toward much more favorable atmospheric conditions over deep warm water. Florence will likely be a hurricane soon.
The expectation remains that a powerful hurricane will approach the southeast or mid-Atlantic coast next Wednesday or Thursday.
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In the far-east Atlantic, Tropical Storm Isaac has formed. It is also expected to intensify into a hurricane, though the environment appears a bit marginal, so the future intensity is uncertain. Isaac is forecast to move due west and is scheduled to reach the Caribbean islands, possibly including those ravaged last hurricane season, about Thursday as well.
Tropical Storm Helene is only of concern to the Cape Verde islands near Africa. After passing those islands, it is expected to turn out to sea. More on Isaac and Helene below.
Florence: The forecast for the next five days appears straightforward. An unusually strong, elongated high pressure cell (a huge bubble of air) will build across the Northeast into the North Atlantic to the north of Florence. This will accelerate the hurricane in the direction of the southeast or southern mid-Atlantic coast. Every indication is that Florence will strengthen into a very powerful hurricane during this time.
That takes us to late Wednesday or early Thursday with Hurricane Florence bearing down on the coast. The Carolinas appear to be the target zone at this point, but Georgia, Virginia and the Delmarva Peninsula need to maintain vigilance as well since the forecast gets difficult in about five days.
Once the storm is off the coast on Wednesday, the steering currents get murky. There are several possibilities.
It appears that Florence will slow down as it turns around the west end of the bubble of high-pressure. That would cause the hurricane, or what's left of it if it moves inland, to slow down. That process could take some days, causing serious inland and coastal flooding, as well as other hazards.
It is also possible that the storm will stall toward the end of the week and meander. Or perhaps it will move slowly north or northeast. The point is, the approach to the coast is just Phase One of this event. There may well be a Phase Two and Phase Three as a slow-moving weaker storm drifts around.
The bottom line is that everybody from Georgia through the Carolinas to Virginia, at the coast and in the eastern part of those states, including Washington, D.C., and nearby cities, should be sure they are ready for extended power outages and dangerous weather conditions, which in some cases will require evacuations. Vigilance is required as far north as Long Island, New York due to the uncertainty in the track late next week.
Remember the rule: Slow-moving storms are notoriously difficult to forecast. It appears that Florence will fall into that category once it gets near or across the coastline.
Expect changes in the forecast for the storm's path late next week. Stay in touch with your local authorities.
North Florida is on the edge of the danger zone. It is not 100 percent certain that Florence will miss Florida. Florence insists on staying a bit farther south than forecast. Even if the center misses to the north, dangerous weather is possible. It's a good time to be sure your hurricane plan is in order, just in case.
Key messages from the National Hurricane Center:
- Florence is forecast to be a dangerous major hurricane near the southeast U.S. coast by late next week, and the risk of direct impacts continues to increase. However, given the uncertainty in track and intensity forecasts at those time ranges, it's too soon to determine the exact timing, location and magnitude of those impacts.
- Interests along the U.S. East Coast, particularly from north Florida through North Carolina, should closely monitor the progress of Florence, ensure they have their hurricane plan in place and follow any advice given by local officials.
- Large swells affecting Bermuda and portions of the U.S. East Coast will continue into next week. These swells will result in life-threatening surf and rip currents.
Elsewhere, a system designated Disturbance No. 94L is located near Bermuda. It is disorganized and will likely be absorbed into the jet stream before it can attain a circulation. Assuming that happens, it will be of no consequence to Florence. The National Hurricane Center gives it only a 10 percent chance of organizing into at least a Tropical Depression. For now, we'll ignore it as a factor in the forecast for Florence.
In addition, there is another system, which has a 20 percent chance of development. It's labeled "potential disturbance." It is of no consequence except related to the steering currents for Helene.
Tropical Storm Isaac has formed from former Tropical Depression No. 9. It appears the high pressure filling in behind Florence will extend far enough south to block this system from turning north, though there is some disagreement about this in the models. The atmospheric conditions do not appear ideal for rapid strengthening, but we often do not have a handle on all of those factors. The upper-level pattern is complicated by upper-level winds related to Florence, Helene and another disturbance expected to form in the middle of the Atlantic.
The bottom line: People in the eastern Caribbean islands need to be ready for a hurricane arriving mid-to-late next week.
After the storm passes through or near the islands late in the week, assuming it does, the path and strength become uncertain. The models generally show a weak system, but the uncertainty is too great to make any specific statements. For now, in Florida, we will watch how things develop in the next few days. Isaac is still almost 3,000 miles away from Miami.
Tropical Storm Helene will pass through the Cape Verde islands Saturday night and Sunday, then turn out to sea. It is expected to reach hurricane strength but not be a threat to the U.S.