FLORIDA
STORMS
Hurricane Sam
LOCATED
1290 MI ESE OF THE NORTHERN LEEWARD ISLANDS
WINDS
85 MPH
PRESSURE
986 MB
MOVING
W AT 12 MPH
From the National Hurricane Center at 500 PM AST Fri Sep 24 2021
Sam's intensification resumes as the hurricane slows its forward motion.
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 PM AST (2100 UTC), the center of Hurricane Sam was located near latitude 12.1 North, longitude 44.8 West. Sam is moving toward the west near 12 mph (19 km/h) and this motion is expected to continue with a gradual decrease in forward speed and turn toward the west northwest over the weekend.

Maximum sustained winds have increased to near 85 mph (140 km/h) with higher gusts. Rapid intensification is forecast over the next several days, and Sam is expected to become a major hurricane on Saturday. 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 986 mb (29.12 inches).

At 500 PM AST (2100 UTC), the center of Hurricane Sam was located near latitude 12.1 North, longitude 44.8 West. Sam is moving toward the west near 12 mph (19 km/h) and this motion is expected to continue with a gradual decrease in forward speed and turn toward the west northwest over the weekend.

Maximum sustained winds have increased to near 85 mph (140 km/h) with higher gusts. Rapid intensification is forecast over the next several days, and Sam is expected to become a major hurricane on Saturday. 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 986 mb (29.12 inches).

Sam's structure on satellite has improved this afternoon, with overshooting cloud tops rotating quickly around the small central dense overcast, providing the appearance that the hurricane is mixing out the dry air that affected its core structure this morning. In fact, the last few visible satellite images suggest that a small eye is clearing out within the cirrus canopy. Interestingly, a recent 1930 UTC SSMIS pass suggests concentric bands are also forming in Sam's core structure and it remains to be seen how that structure will affect the wind field evolution of the hurricane. The latest subjective Dvorak intensities estimates form TAFB and SAB were a consensus T4.5/75 kt, while the latest SATCON and ADT estimates from UW-CIMSS have also increased this afternoon. The current advisory intensity has been set to 75-kt. Given the recent trends on satellite, this may be conservative.

The motion of Sam has remained on the same heading, though the storm is beginning to slow down with the estimate now at 280/10 kt. An additional slowdown in forward motion is anticipated in the short-term as the mid-level ridging shuffles to the northwest of the tropical cyclone, impeding its forward motion. However, after 72 hours, this same ridge is expected to shift back to the northeast of Sam as a deep-layer trough off the Eastern United States coastline becomes established. Track guidance spread increases towards the end of the forecast, with the ECMWF and GFS remaining at odds, with the former on the equatorward side, and the latter on the poleward side of the track envelope. The consensus aids, however, have changed little from the previous advisory and the latest NHC track forecast is quite similar to the previous one.

Now that Sam appears to have mixed out the dry air seen this morning, intensification, likely rapid, is resuming. The only fly in the ointment is the current concentric banding structure on microwave imagery, which hints at the possibility of an eyewall replacement cycle. Assuming the smaller eye will not collapse in the short term, rapid intensification appears likely over the next 12-24 hours and the intensity has been raised in the short term, taking Sam to major hurricane intensity by tomorrow. The latest NHC intensity forecast now shows a slightly higher peak at 120-kt in 48 hours followed by very gradual decay, due to a subtle increase in vertical wind shear, potentially some upwelling effects due to the slow forward notion, and eyewall replacement cycles that could lead to a broadening of the wind field. The latest NHC intensity forecast starts out on the high side of the intensity guidance but ends up very close to the HCCA consensus aid by the end of the forecast period. Regardless of the details, Sam is expected to be a significant hurricane through the forecast period.

Sam's structure on satellite has improved this afternoon, with overshooting cloud tops rotating quickly around the small central dense overcast, providing the appearance that the hurricane is mixing out the dry air that affected its core structure this morning. In fact, the last few visible satellite images suggest that a small eye is clearing out within the cirrus canopy. Interestingly, a recent 1930 UTC SSMIS pass suggests concentric bands are also forming in Sam's core structure and it remains to be seen how that structure will affect the wind field evolution of the hurricane. The latest subjective Dvorak intensities estimates form TAFB and SAB were a consensus T4.5/75 kt, while the latest SATCON and ADT estimates from UW-CIMSS have also increased this afternoon. The current advisory intensity has been set to 75-kt. Given the recent trends on satellite, this may be conservative.

The motion of Sam has remained on the same heading, though the storm is beginning to slow down with the estimate now at 280/10 kt. An additional slowdown in forward motion is anticipated in the short-term as the mid-level ridging shuffles to the northwest of the tropical cyclone, impeding its forward motion. However, after 72 hours, this same ridge is expected to shift back to the northeast of Sam as a deep-layer trough off the Eastern United States coastline becomes established. Track guidance spread increases towards the end of the forecast, with the ECMWF and GFS remaining at odds, with the former on the equatorward side, and the latter on the poleward side of the track envelope. The consensus aids, however, have changed little from the previous advisory and the latest NHC track forecast is quite similar to the previous one.

Now that Sam appears to have mixed out the dry air seen this morning, intensification, likely rapid, is resuming. The only fly in the ointment is the current concentric banding structure on microwave imagery, which hints at the possibility of an eyewall replacement cycle. Assuming the smaller eye will not collapse in the short term, rapid intensification appears likely over the next 12-24 hours and the intensity has been raised in the short term, taking Sam to major hurricane intensity by tomorrow. The latest NHC intensity forecast now shows a slightly higher peak at 120-kt in 48 hours followed by very gradual decay, due to a subtle increase in vertical wind shear, potentially some upwelling effects due to the slow forward notion, and eyewall replacement cycles that could lead to a broadening of the wind field. The latest NHC intensity forecast starts out on the high side of the intensity guidance but ends up very close to the HCCA consensus aid by the end of the forecast period. Regardless of the details, Sam is expected to be a significant hurricane through the forecast period.

Partners of the Florida Public Radio Emergency Network include:  WDNA (Miami), WFIT (Melbourne), WMFE (Orlando), WFSU (Tallahassee), WGCU (Fort Myers), WJCT (Jacksonville), WKGC (Panama City), WLRN (Miami), WMNF (Tampa-Sarasota), WQCS (Fort Pierce), WUFT (Gainesville-Ocala), WUSF (Tampa), WUWF (Pensacola) and Florida Public Media.

1885 Stadium Road

PO Box 118400

Gainesville, FL 32611

(352) 392-5551

Loading...
linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram