PEMBROKE PARK, Fla. – The forecast models have diverged his afternoon on Hurricane Florence's forecast once it gets near or across the coastline.
A Hurricane and storm surge warning is now in effect for most of the South Carolina coast and all of the North Carolina coast. A Hurricane or Tropical Storm Watch is in effect for some of the islands in the eastern Caribbean as well.
Summary: HURRICANE FLORENCE may still strengthen a bit as it heads for the Carolinas and Virginia. It may reach Category 5 strength tonight. There is now an even bigger question mark about how the storm will track when it nears the North Carolina coast. ISAAC is struggling to maintain its strength, but is on track toward the Caribbean at or near hurricane strength. In addition, a disturbance in the western Caribbean is heading for the western Gulf where there is a good chance it will develop into a threat for Texas or Northern Mexico.
FLORENCE is a strong Category 4 hurricane. It went through an internal process called an “eyewall replacement cycle” earlier today whereby it weakened and expanded into a bigger hurricane. Often storms restrengthen after that process, as Florence has done. The current peak winds are estimated at 140 mph – Category 4. It has very warm ocean water and optimal atmospheric conditions ahead of it, which means another strengthening phase is likely.
The forecast is for it to maintain Category 3 or 4 strength as it approaches the Carolina coast on Thursday. Strong hurricanes always fluctuate in intensity, so it is impossible to know exactly how strong Florence will be when it reaches the coast, but the expectation is that it will be an extremely powerful and destructive hurricane. In addition, Florence is expected to expand in size over the next two days. Widespread coastal destruction is expected to be Phase One of this disaster.
The steering currents are well established for now, so there is high confidence that Florence will get near the North or South Carolina coast on Thursday. About that time, the steering currents collapse, however, so for at least a couple of days, maybe more, the hurricane, or a weaker version of the storm, will meander and dump rain. This might happen close to the coast, or well inland.
Phase Two of this disaster will be caused by the slow-moving storm. It will either continuously batter the coast, severely flood inland areas, or more likely, both.
The European model now shows Florence drifting south along the North Carolina and then South Carolina coast for 2 or 3 days before heading inland. The American GFS model shows it stalling briefly over North Carolina, a very different forecast. This puts big question marks on the track after the next two days.
Bear in mind that slow-moving storms are notoriously poorly forecast, so don’t count on any precise track forecasts during or after landfall. In addition, the damaging winds and flooding rain will occur far from the storm’s center, especially to the north, meaning the exact track is not important. Widespread rainfall of 15-25 inches with up to 35 inches in some locations is possible. This part of the eastern U.S. has been saturated by rain this year, so extreme flooding is anticipated.
Here are the Key Messages from the National Hurricane Center concerning Florence:
1. A life-threatening storm surge is now highly likely along portions of the coastlines of South Carolina and North Carolina, and a Storm Surge Warning is in effect for a portion of this area. All interests from South Carolina into the mid-Atlantic region should ensure they have their hurricane plan in place and follow any advice given by local officials.
2. Life-threatening, catastrophic flash flooding and significant river flooding is likely over portions of the Carolinas and Mid-Atlantic states from late this week into early next week, as
Florence is expected to slow down as it approaches the coast and moves inland.
3. Damaging hurricane-force winds are likely along portions of the coasts of South Carolina and North Carolina, and a Hurricane Warning has been issued for a part of this area. Damaging winds could also spread well inland into portions of the Carolinas and Virginia.
4. Large swells affecting Bermuda and portions of the U.S. East Coast will continue this week, resulting in life-threatening surf and rip currents.
TROPICAL STORM ISAAC continues toward the eastern Caribbean Islands – the Lesser Antilles. A Hurricane Watch is in effect for Guadeloupe, Martinique, and Dominica. A Tropical Storm Watch is in effect for islands to the north.
The weather should deteriorate in the islands Wednesday night, with the storm passing through the islands on Thursday. If Isaac stays to the right side of the cone, it could affect Puerto Rico and the surrounding islands after that, though Isaac is a small storm so a near miss would mean little effect on land.
Since Isaac is a small storm, it has the ability to intensify quickly, but also to weaken quickly if the atmospheric conditions become hostile. The upper winds that will impact the track of Isaac are forecast to be fairly hostile, in part thanks to Hurricane Florence to the north. Those winds should keep Isaac from dramatically intensifying, but it is still forecast to reach the islands at or near hurricane strength.
The bottom line is that the eastern Caribbean islands should prepare for the possibility of a hurricane arriving Thursday, but another Hurricane Maria is not in the cards.
After Isaac moves into the Caribbean late Thursday, it is most likely to weaken and continue west. The models diverge somewhat, but most show a much weaker Isaac at that time. It is too early to know for sure what factors might steer Isaac, though usually weaker storms are swept along to the west. We do not see a threat to South Florida at this time.
Here are the Key Messages from the National Hurricane Center concerning Isaac:
1. Isaac is expected to be at or near hurricane intensity when it approaches the Lesser Antilles on Thursday, and hurricane and tropical storm watches have been issued for several islands. Interests in those areas should follow any advice given by their local officials, and warnings will likely be issued this evening.
2. Interests elsewhere in the Lesser Antilles should continue to monitor Isaac during the next couple of days.
The area of disturbed weather in the western Caribbean labeled DISTURBANCE #2 is getting better organized. It will pass over the Yucatan Peninsula of Mexico and then head into the western Gulf. At that time, the upper-level winds are forecast to become reasonably conducive for a Tropical Depression or Tropical Storm to form, although it won’t have much time. Still, along the Texas and northern Mexico coast, residents should be aware that storms can organize and intensify quickly over the warm waters of the Gulf.
HURRICANE HELENE is moving north into the Atlantic and will not affect land.
The system labeled DISTURBANCE #1 may eventually get a name. It will not affect land this week, and probably never will, as it meanders far out in the Atlantic.
