Subtropical Storm Ernesto formed west of the Azores on Wednesday morning. At 11:00 a.m. EDT on Wednesday the center of Subtropical Storm Ernesto was located at latitude 38.1°N and longitude 46.0°W which put it about 695 miles (1120 km) southeast of Cape Race, Newfoundland. Ernesto was moving toward the north at 8 m.p.h. (13 km/h). The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h). The minimum surface pressure was 1008 mb.
More thunderstorms formed closer to the center of a low pressure system west of the Azores on Wednesday morning and the National Hurricane Center designated the system as Subtropical Storm Ernesto. Several bands of showers and thunderstorms wrapped around the eastern and northern portions of the circulation. Bands northwest of the center of Ernesto consisted primarily of showers and lower clouds. The circulation may have been transporting some cooler, drier, more stable air into that part of the circulation. Showers and thunderstorms around the center of Ernesto were generating upper level divergence which was pumping mass away to the northeast of the subtropical storm.
Subtropical Storm Ernesto will move through an environment that could support some intensification during the next day or so. Ernesto will move over water where the Sea Surface Temperature is near 26°C. It will move through a region where the upper level winds are not too strong and there will not be much vertical wind shear. Subtropical Storm Ernesto could strengthen during the next 12 to 24 hours. Ernesto will move over cooler water later on Thursday and it will start to weaken. An upper level trough east of the U.S. will approach Subtropical Storm Ernesto from the west. Southwesterly winds ahead of the trough will cause more vertical wind shear and Ernesto could make a transition to an extratropical cyclone.
The southwesterly winds ahead of the upper level trough will steer Subtropical Storm Ernesto in a general northeasterly direction. On its anticipated track Subtropical Ernesto will pass between the Azores and Greenland.
Former Subtropical Storm Debby made a transition to a tropical storm on Wednesday. At 11:00 a.m. EDT on Wednesday the center of Tropical Storm Debby was located at latitude 41.2°N and longitude 48.3°W which put it about 1150 miles (1855 km) west-northwest of the Azores. Debby was moving toward the northeast at 12 m.p.h. (19 km/h). The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h). The minimum surface pressure was 1003 mb.
The structure of former Subtropical Storm Debby changed on Wednesday and it exhibited the characteristics of a tropical storm. More thunderstorms formed around the center of circulation and those thunderstorms rose higher into the atmosphere. Additional bands of showers and thunderstorms developed and revolved around the core of the circulation. Storms near the core began to generate upper level divergence. The strongest winds occurred closer to the center of circulation. The National Hurricane Center designated Debby as a tropical storm based on information from satellites.
Tropical Storm Debby will move into an environment unfavorable for a tropical storm during the next 24 to 48 hours. Debby was over water where the Sea Surface Temperature was near 26°C, but it will soon move over much cooler water. It will start to weaken when it moves over the cooler water. It could take several days for the circulation around Tropical Storm Debby to spin down.
Tropical Storm Debby will be steered toward the northeast as it moves between an upper level trough to the west and an upper level ridge to the east. On its anticipated track Tropical Storm Debby will move between the Azores and Greenland.
Hurricane Gert intensified to Category 2 on the Saffir-Simpson Scale as it sped over the Gulf Stream south of Nova Scotia on Wednesday afternoon. At 5:00 p.m. EDT on Wednesday the center of Hurricane Gert was located at latitude 38.7°N and longitude 62.4°W which put it about 410 miles (665 km) south of Halifax, Nova Scotia. Gert was moving toward the northeast at 31 m.p.h. (50 km/h). The maximum sustained wind speed was 100 mp.h. (160 km/h) and there were wind gusts to 120 m.p.h. (195 km/h). The minimum surface pressure was 970 mb.
Although Hurricane Gert is at a fairly high latitude, it has the classic structure of a Hurricane. There is a fairly small eye at the center of circulation. The eye is surround by a ring of strong thunderstorm and the strongest winds are occurring in this ring of thunderstorms. There are additional bands of showers and thunderstorms revolving around the core of the hurricane. The circulation is symmetrical and thunderstorms in the core are producing upper level divergence which is pumping away mass to the northeast of the hurricane. Winds to hurricane force extend out about 40 miles (65 km) primarily to the east of the center of circulation. Winds to tropical storm force extend out about 140 miles (225 km) from the center.
Hurricane Gert is moving over the Gulf Stream which means it is moving over water where the Sea Surface Temperature (SST) is near 28.5°C. An upper level trough west of Gert is producing southwesterly winds which are blowing toward the top of the hurricane. However, there is not much change of wind speed with height, which means that there is little vertical wind shear. The combination of the warm water of the Gulf Stream and little vertical shear, allowed Hurricane Gert to strengthen on Wednesday.
Hurricane Gert could intensify during the next few hours, but it will soon move into a much less favorable environment. Gert will soon move north of the Gulf Stream where the SSTs are much cooler. The upper level trough is moving closer to Hurricane Gert and the winds are the upper level are forecast to get stronger. When those winds increase, there will be much more vertical wind shear. Colder water and more wind shear will cause Hurricane Gert to weaken on Thursday. Gert could make a transition to an extratropical cyclone in colder environment of the North Atlantic.
Southwesterly winds in the upper level trough are steering Hurricane Gert quickly toward the northeast and that general motion is expected to continue. On its anticipated track, Hurricane Gert will move south of Labrador and Greenland.
Even as Hurricane Gert speeds away over the North Atlantic three new tropical waves over the tropical Atlantic have the potential to develop into tropical cyclones. A tropical wave about 800 miles (1290 km) east of the Lesser Antilles designated as Invest 91L showed signs of organization on Wednesday. A few more thunderstorms developed closed to the center of circulation. A reconnaissance plane is scheduled to investigate this system on Thursday. A little farther to the east another tropical wave designated Invest 92L was also showing evidence or more organization. A third tropical wave just west of Africa also has the potential to develop during the next few days.
Tropical Storm Alex weakened to just below hurricane intensity as it moved across the Azores on Friday morning. At 10:00 a.m. EST the center of Hurricane Alex was located at latitude 39.3°N and longitude 27.0°W which put it about 35 miles north of Terceira in the Azores. Alex was moving toward the north at 28 m.p.h. (44 km/h). The maximum sustained wind speed was 70 m.p.h. (115 km/h) and there were wind gusts to 85 m.p.h. (135 km/h). The minimum surface pressure was 986 mb.
It appears that the center of Tropical Storm Alex made landfall on the island of Terceira. Weather stations on Santa Maria and Sao Miguel have measured tropical storm force winds. However, it seems like the core of Tropical Storm Alex which contains the strongest winds remained over water. Higher wind speeds most likely occurred on the windward sides of mountains in the Azores.
In anticipation of the movement of Tropical Storm Alex away from the islands all Hurricane Warnings and Tropical Storm Warnings for the Azores have been discontinued.
Tropical Storm Alex is over water where the Sea Surface Temperature is near 16°C. It will move over even cooler water and Alex will soon be unable to extract enough energy from the ocean to sustain the structure of a tropical cyclone. The structure of Alex will gradually change to the structure of a cold core extratropical cyclone during the next several days. It is likely to maintain much of its intensity as it moves through the extratropical transition.
An upper level trough is steering Tropical Storm Alex toward the north-northwest and a general northwesterly motion is expected to continue for the next two or three days. Tropical Storm Alex could end up south of Greenland over the weekend as a strong extratropical cyclone.