The low pressure system that was Tropical Storm Hermine began to move back toward the west on Monday and the motion brought it closer to Long Island. At 8:00 p.m. EDT on Monday the center of Post Tropical Storm Hermine was located at latitude 39.3°N and longitude 70.3°W which put it about 135 miles south of Nantucket Island. Hermine was moving toward the west-northwest at 9 m.p.h. (15 km/h). The maximum sustained wind speed was 70 m.p.h. (110 km/h) and there were wind gusts to 85 m.p.h. (135 km/h). The minimum surface pressure was 997 mb.
A Tropical Storm Warning remains in effect for the portion of the coast from Fire Island Inlet to Port Jefferson Harbor on Long Island and from New Haven, Connecticut to Sagamore Beach, Massachusetts including Block Island, Martha’s Vineyeard and Nantucket Island. Most of the stronger winds are occurring over water, but a weather station at Nantucket, Massachusetts reported a sustained wind speed of 44 m.p.h. (71 km/h) and a wind gust ot 56 m.p.h. (90 km/h) on Monday.
Post Tropical Storm Hermine has not had the structure of a tropical cyclone for several days. There are no thunderstorms near the center of circulation. The taller clouds are all occurring west of the center. The circulation pulled in drier air which has circulated into the core of the circulation. An upper level low south of Hermine has generated southeasterly winds which are blowing across the top of the circulation. The vertical wind shear combined with the drier air to prevent the development of new thunderstorms near the center of circulation.
The environment around Post Tropical Storm Hermine could become a little less hostile on Tuesday. It will be moving over water where the Sea Surface Temperature (SST) is near 25.5°C. As Hermine moves west the vertical wind shear will decrease. However, the cyclone is surrounded by dry air. If the surface low moves west, the complex environment could allow the system to maintain its intensity for another day or so. If the surface low moves farther north, it will move over cooler SSTs and the wind speeds will decrease.
The upper low to the south of Post Tropical Storm Hermine and a ridge north of Hermine are combining to steer it toward the west-northwest. That general motion is expected to continue for a few more hours. As Post Tropical Storm Hermine interacts with the upper low, it could make a slow cyclonic loop. On its expected track Hermine could move closer to Long Island on Tuesday.
Post Tropical Storm Hermine will continue to produce modest water rises along the coast. In addition persistent wind and wave action will generate more beach erosion.
Tropical Storm Hermine strengthened on Wednesday evening and a Hurricane Warning was issued for a portion of the northern Florida coast. A Hurricane Warning was in effect for the portion of the coast from Suwannee River to Mexico Beach, Florida. A Hurricane Watch and a Tropical Storm Warning was in effect for the portions of the coast from Anclote River to Suwannee River and from Mexico Beach to Destin, Florida. The Tropical Storm Watch was extended farther up the Mid-Atlantic coast. The Tropical Storm Watch was in effect for the portion of the coast from Marineland, Florida to South Santee River, South Carolina.
At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Hermine was located at latitude 25.8°N and longitude 87.0°W which put it about 295 miles (475 km) south-southwest of Apalachicola, Florida. Hermine was moving toward the north-northeast at 10 m.p.h. (16 km/h). The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h). The minimum surface pressure was 998 mb.
The circulation of Tropical Storm Hermine became better organized on Wednesday, but it is still not really well organized. A tighter center of circulation developed. However, the wind field is still asymmetrical. The stronger winds are mainly east of the center and the winds are weaker in the western half of the circulation. An area of strong thunderstorms developed near the center and another cluster of thunderstorms persisted southwest of the center. There are not many thunderstorms northwest of the center. There are some spiral rainbands, but they are fragmented.
Tropical Storm Hermine is in an environment that is favorable for intensification. It is moving over water where the Sea Surface Temperature is near 30°C. The upper level flow pattern is enhancing the divergence of mass to the northeast of Hermine. The enhanced upper level divergence pumped out enough mass to allow the surface pressure to decrease by a few millibars on Wednesday evening. Tropical Storm Hermine is expected to continue to intensify on Thursday and it should become a hurricane before it makes landfall on Thursday night.
The upper level ridge that was blocking a northward motion of Hermine has weakened. So, the tropical storm has begun to more toward the north-northeast. An upper level trough is expected to steer Hermine a little faster toward the northeast on Thursday. On its anticipated track Hermine could make landfall somewhere between Apalachicola and Tarpon Springs, Florida on Thursday night. After it moves across northeast Florida, Hermine could move near the coast of Carolinas on Friday.
Hermine is likely to be a hurricane when it makes landfall on Thursday night. The core of the circulation which will contain the highest winds is likely to be fairly small and Hermine is likely to cause localized minor wind damage. There will undoubtedly be power outages. The coastline around the northeastern Gulf of Mexico is vulnerable to storm surges and Hermine will also produce a storm surge which could range up to 7 to 8 feet (2 to 2.5 meters) near where the center crosses the coast. The storm surge will be less farther away from where the center makes landfall. In addition Hermine will generate locally heavy rain which could cause fresh water flooding. Directional wind shear associated with rainbands moving inland could spin up tornadoes in the eastern half of Hermine.