FLORIDA
STORMS
Hurricane Sam
LOCATED
1150 MI ESE OF THE NORTHERN LEEWARD ISLANDS
WINDS
110 MPH
PRESSURE
973 MB
MOVING
WNW AT 13 MPH
From the National Hurricane Center at 500 AM AST Sat Sep 25 2021
Sam almost a major hurricane.
TAP LINKS BELOW TO FOCUS
Alerts
hazards
summary
DISCUSSION

There are no coastal watches or warnings in effect.

There are no coastal watches or warnings in effect.

None.

None.

At 500 AM AST (0900 UTC), the eye of Hurricane Sam was located near latitude 12.8 North, longitude 46.7 West. Sam is moving toward the west northwest near 13 mph (20 km/h). A slower motion to the west northwest is expected over the weekend, followed by a turn to the northwest on Monday. Maximum sustained winds have increased to near 110 mph (175 km/h) with higher gusts. Additional strengthening is forecast, and Sam is expected to become a major hurricane later today. Sam is a small hurricane. Hurricane force winds extend outward up to 15 miles (30 km) from the center and tropical storm force winds extend outward up to 60 miles (95 km). The estimated minimum central pressure is 973 mb (28.74 inches).

At 500 AM AST (0900 UTC), the eye of Hurricane Sam was located near latitude 12.8 North, longitude 46.7 West. Sam is moving toward the west northwest near 13 mph (20 km/h). A slower motion to the west northwest is expected over the weekend, followed by a turn to the northwest on Monday. Maximum sustained winds have increased to near 110 mph (175 km/h) with higher gusts. Additional strengthening is forecast, and Sam is expected to become a major hurricane later today. Sam is a small hurricane. Hurricane force winds extend outward up to 15 miles (30 km) from the center and tropical storm force winds extend outward up to 60 miles (95 km). The estimated minimum central pressure is 973 mb (28.74 inches).

Sam continues to rapidly intensify. Geostationary satellite and microwave images show that the storm has a very small and distinct eye surrounded by a nearly symmetric ring of cold cloud tops. The latest Dvorak estimates range from 90 to 102 kt, and based on that data, the initial intensity is increased to 95 kt. Although Sam is nearly a major hurricane, it remains quite compact with tropical-storm-force and hurricane-force winds estimated to only extend 50 n mi and 15 n mi from the center, respectively.

The hurricane is moving west-northwestward at 11 kt and is currently being steered by a mid-level ridge to its north. There has been little change to the track forecast philosophy or model guidance. Sam is expected to continue west-northwestward during the next two or three days, but it is forecast to move at a notably slower pace of 6-8 kt during most of that time period. After that time, the ridge is expected to shift eastward as a deep-layer trough becomes established over the western Atlantic. This change in the steering pattern should cause Sam to turn northwestward and speed up some by the middle of next week. The models are in fairly good agreement, and the NHC track forecast is largely an update of the previous one. Based on this forecast, and nearly all of the reliable guidance, Sam is expected to still be well to the east or northeast of the northern Leeward Islands through day 5.

Continued steady or rapid strengthening is expected during the next day or two as the hurricane remains in near ideal conditions of very low wind shear and warm 29 deg C waters. However, beyond that time the shear is expected to increase a little, and that will likely cause Sam to level off in strength or weaken slightly next week. The NHC intensity forecast is slightly above the models in the short term, given the impressive structure of the hurricane and favorable conditions, but falls in line with the consensus aids at the longer lead times. Regardless of how strong Sam gets, nearly all of the models indicate that it will remain a powerful hurricane during the next several days.

Sam has continued to intensify this morning and now has a complete ring of deep convection with cloud tops colder than -70 degrees C surrounding a mostly clear, small eye. The latest subjective Dvorak intensity estimates from TAFB and SAB are both 102 kt, while the combined objective Dvorak intensity estimates from the UW-CIMSS SATCON and ADT is 110 kt. Based on this data, the initial intensity has been increased to 105 kt for this advisory, making Sam a major hurricane. The cyclone remains compact, with hurricane-force winds extending only 20 n mi from the center.

The hurricane wobbled to the west over the past few hours. However, the 12-hour motion is west-northwest at 9 kt. There are no changes to the forecast track reasoning. The ridge the north of Sam responsible for its current motion is forecast to shift to the east in a couple of days as a deep-layer trough establishes itself over the western Atlantic. Sam is forecast to turn northwestward around the southwestern periphery of the ridge in about 48 h, and gradually increase its forward speed thereafter. The model guidance continues to be in very good agreement with this scenario, and the latest NHC track forecast is unchanged from the previous one. It should be noted that the westernmost guidance continues to be the ECMWF ensemble mean, whose members have had a low bias in the intensity of Sam, which is likely contributing to the westward track bias. Based on the NHC forecast, and all of the other guidance, Sam is expected to still be well to the east or northeast of the northern Leeward Islands through day 5.

Environmental conditions support further strengthening in the short term, and Sam is expected to become a category 4 hurricane by Sunday. In a few days, some southwesterly shear is forecast to develop as the cyclone begins to round the periphery of the subtropical ridge. Although this should cause Sam to weaken, it is still expected to remain a powerful hurricane throughout the 5-day forecast period. The latest NHC intensity forecast is near the previous one, which remains slightly above the various consensus solutions through 72 h, and then closely follows the consensus thereafter.

Sam continues to rapidly intensify. Geostationary satellite and microwave images show that the storm has a very small and distinct eye surrounded by a nearly symmetric ring of cold cloud tops. The latest Dvorak estimates range from 90 to 102 kt, and based on that data, the initial intensity is increased to 95 kt. Although Sam is nearly a major hurricane, it remains quite compact with tropical-storm-force and hurricane-force winds estimated to only extend 50 n mi and 15 n mi from the center, respectively.

The hurricane is moving west-northwestward at 11 kt and is currently being steered by a mid-level ridge to its north. There has been little change to the track forecast philosophy or model guidance. Sam is expected to continue west-northwestward during the next two or three days, but it is forecast to move at a notably slower pace of 6-8 kt during most of that time period. After that time, the ridge is expected to shift eastward as a deep-layer trough becomes established over the western Atlantic. This change in the steering pattern should cause Sam to turn northwestward and speed up some by the middle of next week. The models are in fairly good agreement, and the NHC track forecast is largely an update of the previous one. Based on this forecast, and nearly all of the reliable guidance, Sam is expected to still be well to the east or northeast of the northern Leeward Islands through day 5.

Continued steady or rapid strengthening is expected during the next day or two as the hurricane remains in near ideal conditions of very low wind shear and warm 29 deg C waters. However, beyond that time the shear is expected to increase a little, and that will likely cause Sam to level off in strength or weaken slightly next week. The NHC intensity forecast is slightly above the models in the short term, given the impressive structure of the hurricane and favorable conditions, but falls in line with the consensus aids at the longer lead times. Regardless of how strong Sam gets, nearly all of the models indicate that it will remain a powerful hurricane during the next several days.

Sam has continued to intensify this morning and now has a complete ring of deep convection with cloud tops colder than -70 degrees C surrounding a mostly clear, small eye. The latest subjective Dvorak intensity estimates from TAFB and SAB are both 102 kt, while the combined objective Dvorak intensity estimates from the UW-CIMSS SATCON and ADT is 110 kt. Based on this data, the initial intensity has been increased to 105 kt for this advisory, making Sam a major hurricane. The cyclone remains compact, with hurricane-force winds extending only 20 n mi from the center.

The hurricane wobbled to the west over the past few hours. However, the 12-hour motion is west-northwest at 9 kt. There are no changes to the forecast track reasoning. The ridge the north of Sam responsible for its current motion is forecast to shift to the east in a couple of days as a deep-layer trough establishes itself over the western Atlantic. Sam is forecast to turn northwestward around the southwestern periphery of the ridge in about 48 h, and gradually increase its forward speed thereafter. The model guidance continues to be in very good agreement with this scenario, and the latest NHC track forecast is unchanged from the previous one. It should be noted that the westernmost guidance continues to be the ECMWF ensemble mean, whose members have had a low bias in the intensity of Sam, which is likely contributing to the westward track bias. Based on the NHC forecast, and all of the other guidance, Sam is expected to still be well to the east or northeast of the northern Leeward Islands through day 5.

Environmental conditions support further strengthening in the short term, and Sam is expected to become a category 4 hurricane by Sunday. In a few days, some southwesterly shear is forecast to develop as the cyclone begins to round the periphery of the subtropical ridge. Although this should cause Sam to weaken, it is still expected to remain a powerful hurricane throughout the 5-day forecast period. The latest NHC intensity forecast is near the previous one, which remains slightly above the various consensus solutions through 72 h, and then closely follows the consensus thereafter.

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