FLORIDA
STORMS
Hurricane Sam
LOCATED
350 MI ENE OF THE NORTHERN LEEWARD ISLANDS
WINDS
145 MPH
PRESSURE
940 MB
MOVING
NW AT 12 MPH
From the National Hurricane Center at 1100 PM AST Wed Sep 29 2021
Sam gaining strength and size over the western Atlantic.
TAP LINKS BELOW TO FOCUS
key messages
Alerts
hazards
summary
DISCUSSION

1. Swells generated by Sam will impact the Lesser Antilles during the next several days. Swells are expected to reach Bermuda and the Bahamas in a day or so, and then spread to the United States east coast by this weekend. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office.

2. A Tropical Storm Watch could be required for Bermuda on Thursday, and interests there should monitor the progress of Sam.

1. Swells generated by Sam will impact the Lesser Antilles during the next several days. Swells are expected to reach Bermuda and the Bahamas in a day or so, and then spread to the United States east coast by this weekend. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office.

2. A Tropical Storm Watch could be required for Bermuda on Thursday, and interests there should monitor the progress of Sam.

There are no coastal watches or warnings in effect. Interests in Bermuda should monitor the progress of Sam. A Tropical Storm Watch could be required for the island on Thursday.

There are no coastal watches or warnings in effect. Interests in Bermuda should monitor the progress of Sam. A Tropical Storm Watch could be required for the island on Thursday.

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 during the next several days. Swells are expected to reach Bermuda and the Bahamas in a day or so, and then spread to the United States east coast by this weekend. 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 during the next several days. Swells are expected to reach Bermuda and the Bahamas in a day or so, and then spread to the United States east coast by this weekend. These swells could cause life threatening surf and rip current conditions. Please consult products from your local weather office.

At 1100 PM AST (0300 UTC), the center of Hurricane Sam was located near latitude 20.6 North, longitude 58.4 West. Sam is moving toward the northwest near 12 mph (19 km/h), and this general motion with an increase in forward speed is expected during the next couple of days. A turn toward the north and northeast is anticipated by Friday night. On the forecast track, Sam will continue to pass well to the east northeast of the northern Leeward Islands through tonight, and pass to the east of Bermuda early Saturday. Data from a NOAA Hurricane Hunter aircraft indicate that maximum sustained winds have increased to near 145 mph (230 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, with more significant weakening anticipated over the weekend. Hurricane force winds extend outward up to 65 miles (100 km) from the center and tropical storm force winds extend outward up to 150 miles (240 km). The estimated minimum central pressure based on NOAA Hurricane Hunter data is 940 mb (27.76 inches).

At 1100 PM AST (0300 UTC), the center of Hurricane Sam was located near latitude 20.6 North, longitude 58.4 West. Sam is moving toward the northwest near 12 mph (19 km/h), and this general motion with an increase in forward speed is expected during the next couple of days. A turn toward the north and northeast is anticipated by Friday night. On the forecast track, Sam will continue to pass well to the east northeast of the northern Leeward Islands through tonight, and pass to the east of Bermuda early Saturday. Data from a NOAA Hurricane Hunter aircraft indicate that maximum sustained winds have increased to near 145 mph (230 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, with more significant weakening anticipated over the weekend. Hurricane force winds extend outward up to 65 miles (100 km) from the center and tropical storm force winds extend outward up to 150 miles (240 km). The estimated minimum central pressure based on NOAA Hurricane Hunter data is 940 mb (27.76 inches).

Sam is intensifying tonight after completing an eyewall replacement cycle. A recent NOAA Hurricane Hunter aircraft showed peak 700 mb flight-level winds of 138 kt, multiple SFMR surface winds of 120 kt or greater, plus falling central pressure to about 940 mb. This deepening trend is also seen on recent satellite imagery, with significant warming within the eye noted. These data support raising the initial intensity to 125 kt for this advisory. It is of note that the NOAA mission has been quite helpful for both the size and intensity analysis, with dropsondes and SFMR data showing that the hurricane has grown quite a bit since earlier today, mostly on the eastern side. Additionally, reflectivity data from the core confirmed the end of the eyewall replacement cycle.

The hurricane could strengthen a little more overnight while it moves over a warm ocean eddy in fairly light shear. Afterward, gradually cooling SSTs, falling ocean heat content, and the inevitable future eyewall replacement cycles should cause a weakening trend. However, this will likely not be as steady as shown below, and significant deviations (upward or downward) from the forecast can be expected. Faster weakening is expected by the weekend due to cool SSTs and increasing shear. The new forecast is close to the intensity consensus, and is a little higher than the previous NHC prediction early on, primarily due to the initial wind speed.

Sam has sped up tonight, now estimated at 315/10 kt. It sounds like a broken record, but there are no changes to the forecast during the first few days as model guidance is in excellent agreement on a gradually rightward-curving track, passing a couple of hundred n mi or more east of Bermuda. Afterward, guidance is actually in worse agreement over the weekend, with widely divergent solutions from an upper-level trough picking up Sam and turning it north toward Newfoundland or the trough leaving Sam behind, causing a slow eastward motion. The trend in the guidance is for a slower motion at long range, so I've elected to keep the day 4 and 5 points almost the same as the previous advisory, just a hair faster than the latest consensus aids.

Sam is intensifying tonight after completing an eyewall replacement cycle. A recent NOAA Hurricane Hunter aircraft showed peak 700 mb flight-level winds of 138 kt, multiple SFMR surface winds of 120 kt or greater, plus falling central pressure to about 940 mb. This deepening trend is also seen on recent satellite imagery, with significant warming within the eye noted. These data support raising the initial intensity to 125 kt for this advisory. It is of note that the NOAA mission has been quite helpful for both the size and intensity analysis, with dropsondes and SFMR data showing that the hurricane has grown quite a bit since earlier today, mostly on the eastern side. Additionally, reflectivity data from the core confirmed the end of the eyewall replacement cycle.

The hurricane could strengthen a little more overnight while it moves over a warm ocean eddy in fairly light shear. Afterward, gradually cooling SSTs, falling ocean heat content, and the inevitable future eyewall replacement cycles should cause a weakening trend. However, this will likely not be as steady as shown below, and significant deviations (upward or downward) from the forecast can be expected. Faster weakening is expected by the weekend due to cool SSTs and increasing shear. The new forecast is close to the intensity consensus, and is a little higher than the previous NHC prediction early on, primarily due to the initial wind speed.

Sam has sped up tonight, now estimated at 315/10 kt. It sounds like a broken record, but there are no changes to the forecast during the first few days as model guidance is in excellent agreement on a gradually rightward-curving track, passing a couple of hundred n mi or more east of Bermuda. Afterward, guidance is actually in worse agreement over the weekend, with widely divergent solutions from an upper-level trough picking up Sam and turning it north toward Newfoundland or the trough leaving Sam behind, causing a slow eastward motion. The trend in the guidance is for a slower motion at long range, so I've elected to keep the day 4 and 5 points almost the same as the previous advisory, just a hair faster than the latest consensus aids.

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