Monthly Archives: September 2016

Tropical Storm Hermine Strengthens, Hurricane Warning Issued

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.

Large Hurricane Gaston Prompts Tropical Storm Watch for Azores

Large Hurricane Gaston starting moving more quickly toward the northeast on Wednesday and it prompted a Tropical Storm Watch for some of the Azores.  The Tropical Storm Watch includes Flores, Corvo, Faial, Pico Gracsiosa, Sao Jorge and Terceira in the Azores.

At 8:00 p.m. EDT on Wednesday the center of Hurricane Gaston was located at latitude 35.6°N and longitude 46.5°W which put it about 1000 miles (1610 km) west of Faial in the Azores.  Gaston was  moving toward the northeast at 18 m.p.h. (30 km/h).  The maximum sustained wind speed was 105 m.p.h. (165 km/h) and there were wind gusts to 125 m.p.h. (200 km/h).  The minimum surface pressure was 969 mb.

Hurricane Gaston has a large circular eye with a diameter of 35 miles (55 km).  The eye is surrounded by a nearly complete eyewall, although the eyewall is thinner in the southwestern quadrant.  Winds to hurricane force extend out about 45 miles (70 km) from the center.  Hurricane Gaston has characteristics of an annular hurricane and the surrounding rainbands are mainly comprised of showers and shallow clouds.  The upper level divergence is inhibited over the southwestern past of the circulation, but divergence is still occurring north and east of the center.

Hurricane Gaston will be moving through an environment that will become increasingly unfavorable.  It is currently over water where the Sea Surface Temperature (SST) is near 27.5°C, but it will be moving over cooler SST during the next few days.  An upper level trough is producing southwesterly winds which are causing vertical wind shear.  The strength of the upper level winds is expected to increase.  The combination of cooler SSTs and more wind shear will weaken Gaston during the next few days.

Hurricane Gaston is being steering toward the northeast by the westerly flow in the middle latitudes.  That general motion is expected to continue.  On its anticipated track Hurricane Gaston could reach the western Azores within 48 hours.  It is expected to weaken below hurricane intensity by that time.  Because of its large size, Gaston could bring wind and rain to many of the Azores.