FLORIDA
STORMS
Hurricane Sam
LOCATED
610 MI E OF THE NORTHERN LEEWARD ISLANDS
WINDS
130 MPH
PRESSURE
953 MB
MOVING
NW AT 9 MPH
From the National Hurricane Center at 500 AM AST Tue Sep 28 2021
Air force hurricane hunters find Sam has strengthened.
TAP LINKS BELOW TO FOCUS
key messages
Alerts
hazards
summary
DISCUSSION

1. Large swells generated by Sam are affecting the Leeward Islands and will spread to portions of the Virgin Islands, Puerto Rico, Hispaniola, the Bahamas, and Bermuda by Thursday or Friday. Significant swells will likely reach the east coast of the United States and Atlantic Canada by the weekend. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the advice of lifeguards and local officials through the upcoming weekend.

1. Large swells generated by Sam are affecting the Leeward Islands and will spread to portions of the Virgin Islands, Puerto Rico, Hispaniola, the Bahamas, and Bermuda by Thursday or Friday. Significant swells will likely reach the east coast of the United States and Atlantic Canada by the weekend. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the advice of lifeguards and local officials through the upcoming weekend.

There are no coastal watches or warnings in effect.

There are no coastal watches or warnings in effect.

Key messages for Sam can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT3 and WMO header WTNT43 KNHC.

SURF: Swells generated by Sam will impact the Lesser Antilles for the next several days. Swells are expected to reach Bermuda and the Bahamas in a couple of days, and then spread to the United States east coast late this week. These swells could cause life threatening surf and rip current conditions. Please consult products from your local weather office.

Key messages for Sam can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT3 and WMO header WTNT43 KNHC.

SURF: Swells generated by Sam will impact the Lesser Antilles for the next several days. Swells are expected to reach Bermuda and the Bahamas in a couple of days, and then spread to the United States east coast late this week. These swells could cause life threatening surf and rip current conditions. Please consult products from your local weather office.

At 500 AM AST (0900 UTC), the center of Hurricane Sam was located near latitude 17.2 North, longitude 53.9 West. Sam is moving toward the northwest near 9 mph (15 km/h), and this motion is expected to continue for the next few days, with an increase in forward speed beginning on Thursday. A turn toward the north is expected by Friday. On the forecast track, Sam will pass well to the northeast of the northern Leeward Islands on Wednesday and Thursday. Data from an Air Force Reserve Hurricane Hunter aircraft indicate that maximum sustained winds have increased to near 130 mph (215 km/h) with higher gusts. Sam is a category 4 hurricane on the Saffir Simpson Hurricane Wind Scale. Some fluctuations in intensity are expected during the next couple of days, but Sam is forecast to remain a major hurricane through late this week. Hurricane force winds extend outward up to 40 miles (65 km) from the center and tropical storm force winds extend outward up to 125 miles (205 km). The estimated minimum central pressure based on dropsonde data from the aircraft is 953 mb (28.15 inches).

At 500 AM AST (0900 UTC), the center of Hurricane Sam was located near latitude 17.2 North, longitude 53.9 West. Sam is moving toward the northwest near 9 mph (15 km/h), and this motion is expected to continue for the next few days, with an increase in forward speed beginning on Thursday. A turn toward the north is expected by Friday. On the forecast track, Sam will pass well to the northeast of the northern Leeward Islands on Wednesday and Thursday. Data from an Air Force Reserve Hurricane Hunter aircraft indicate that maximum sustained winds have increased to near 130 mph (215 km/h) with higher gusts. Sam is a category 4 hurricane on the Saffir Simpson Hurricane Wind Scale. Some fluctuations in intensity are expected during the next couple of days, but Sam is forecast to remain a major hurricane through late this week. Hurricane force winds extend outward up to 40 miles (65 km) from the center and tropical storm force winds extend outward up to 125 miles (205 km). The estimated minimum central pressure based on dropsonde data from the aircraft is 953 mb (28.15 inches).

The Air Force Reserve Hurricane Hunters that investigated Sam early this morning found evidence that the hurricane has strengthened. Peak 700-mb flight-level winds of 126 kt were reported in the northeastern quadrant, which after the standard adjustment would support an intensity of 110-115 kt. Satellite data also indicate that Sam's structure has improved overnight. Sam's inner core appears to have consolidated into a single, primary eyewall in recent GMI and AMSR2 microwave imagery, and the latest GOES-16 infrared imagery shows a colder ring of convective cloud tops developing around the eye of Sam. This has brought the latest UW-CIMSS ADT and SATCON estimates up to around 115 kt. Based on the flight-level wind data and ongoing satellite trends, the initial intensity is raised to 115 kt for this advisory. The minimum central pressure of 953 mb is based on a center dropsonde of 954 mb with 12-kt surface winds.

In the short-term, internal dynamic processes that are difficult to predict could cause some fluctuations in Sam's intensity. If Sam's eyewall is able to contract today, some additional strengthening could occur, and this possibility is reflected in the latest NHC intensity forecast. Thereafter, the warm sea-surface temperatures and weak to moderate vertical wind shear along Sam's forecast track suggest it should remain a major hurricane for the next several days. Thus, the NHC forecast only shows gradual weakening through 72-96 h, in agreement with the consensus aids IVCN and HCCA. By days 4-5, increasing southerly wind shear along with decreasing SSTs should increase Sam's rate of weakening as it recurves deeper into the mid-latitudes.

Aircraft and microwave data indicate that Sam is slightly tilted in the vertical, with the low-level center displaced just a bit to the south of the mid-level eye. Based on recent aircraft fixes, Sam's initial motion is northwestward, or 310/8 kt. This motion is expected to continue for the next few days as Sam moves around the southwestern periphery of the subtropical ridge. A mid- to upper-level trough is forecast to dig southward over the western Atlantic later this week, which should steer Sam toward the north by Friday. Then, Sam is expected to accelerate north-northeastward within the deep-layer southerly flow ahead of the trough this weekend. The official NHC track forecast is very similar to the previous one, with just a slight adjustment to the left based on the latest track guidance consensus aids. The along-track spread in the guidance noticeably increases as Sam recurves over the western Atlantic, with the ECMWF much slower than the GFS. Once again, the NHC forecast trends closer to the faster GFS solution at longer ranges, given its better overall performance this season.

The Air Force Reserve Hurricane Hunters that investigated Sam early this morning found evidence that the hurricane has strengthened. Peak 700-mb flight-level winds of 126 kt were reported in the northeastern quadrant, which after the standard adjustment would support an intensity of 110-115 kt. Satellite data also indicate that Sam's structure has improved overnight. Sam's inner core appears to have consolidated into a single, primary eyewall in recent GMI and AMSR2 microwave imagery, and the latest GOES-16 infrared imagery shows a colder ring of convective cloud tops developing around the eye of Sam. This has brought the latest UW-CIMSS ADT and SATCON estimates up to around 115 kt. Based on the flight-level wind data and ongoing satellite trends, the initial intensity is raised to 115 kt for this advisory. The minimum central pressure of 953 mb is based on a center dropsonde of 954 mb with 12-kt surface winds.

In the short-term, internal dynamic processes that are difficult to predict could cause some fluctuations in Sam's intensity. If Sam's eyewall is able to contract today, some additional strengthening could occur, and this possibility is reflected in the latest NHC intensity forecast. Thereafter, the warm sea-surface temperatures and weak to moderate vertical wind shear along Sam's forecast track suggest it should remain a major hurricane for the next several days. Thus, the NHC forecast only shows gradual weakening through 72-96 h, in agreement with the consensus aids IVCN and HCCA. By days 4-5, increasing southerly wind shear along with decreasing SSTs should increase Sam's rate of weakening as it recurves deeper into the mid-latitudes.

Aircraft and microwave data indicate that Sam is slightly tilted in the vertical, with the low-level center displaced just a bit to the south of the mid-level eye. Based on recent aircraft fixes, Sam's initial motion is northwestward, or 310/8 kt. This motion is expected to continue for the next few days as Sam moves around the southwestern periphery of the subtropical ridge. A mid- to upper-level trough is forecast to dig southward over the western Atlantic later this week, which should steer Sam toward the north by Friday. Then, Sam is expected to accelerate north-northeastward within the deep-layer southerly flow ahead of the trough this weekend. The official NHC track forecast is very similar to the previous one, with just a slight adjustment to the left based on the latest track guidance consensus aids. The along-track spread in the guidance noticeably increases as Sam recurves over the western Atlantic, with the ECMWF much slower than the GFS. Once again, the NHC forecast trends closer to the faster GFS solution at longer ranges, given its better overall performance this season.

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