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000
ABNT20 KNHC 280515
TWOAT

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
200 AM EDT Tue Sep 28 2021

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Hurricane
Sam, located several hundred miles east of the northern Leeward
Islands.

A broad area of low pressure located several hundred miles
southwest of the Cabo Verde Islands is producing a large area of
disorganized showers and thunderstorms. Environmental conditions are
conducive for further development, and a tropical depression is
likely to form during the next day or two while the system moves
westward to west-northwestward at 5 to 10 mph over the central
tropical Atlantic.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 5 days...high...90 percent.

A tropical wave located over the far eastern tropical Atlantic
several hundred miles southeast of the Cabo Verde Islands continues
to produce a large area of disorganized showers and thunderstorms.
Upper-level winds are conducive for gradual development, and a
tropical depression is likely to form in a day or two while the
disturbance moves westward to west-northwestward at 10 to 15 mph
over the far eastern tropical Atlantic.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 5 days...high...90 percent.

A well-defined low pressure area associated with the remnants
of Peter is located a few hundred miles east of Bermuda. The shower
and thunderstorm activity associated with this system has become
less organized since early Monday. Although strong upper-level
winds are likely to prevent significant development, this system
could still become a short-lived tropical depression later today or
tonight while it moves northeastward at about 10 mph. By Wednesday,
however, conditions are expected to become unfavorable for further
development.
* Formation chance through 48 hours...medium...50 percent.
* Formation chance through 5 days...medium...50 percent.

$$
Forecaster Brown

Summary for Hurricane Sam (AT3/AL182021)

...AIR FORCE HURRICANE HUNTERS FIND SAM HAS STRENGTHENED...
 As of 5:00 AM AST Tue Sep 28
 the center of Sam was located near 17.2, -53.9
 with movement NW at 9 mph.
 The minimum central pressure was 953 mb
 with maximum sustained winds of about 130 mph.

Hurricane Sam Public Advisory Number 23

Issued at 500 AM AST Tue Sep 28 2021  

000
WTNT33 KNHC 280842
TCPAT3
 
BULLETIN
Hurricane Sam Advisory Number  23
NWS National Hurricane Center Miami FL       AL182021
500 AM AST Tue Sep 28 2021
 
...AIR FORCE HURRICANE HUNTERS FIND SAM HAS STRENGTHENED...
 
 
SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...17.2N 53.9W
ABOUT 610 MI...980 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...130 MPH...215 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 9 MPH...15 KM/H
MINIMUM CENTRAL PRESSURE...953 MB...28.15 INCHES
 
 
WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.
 
 
DISCUSSION AND OUTLOOK
----------------------
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).
 
 
HAZARDS AFFECTING LAND
----------------------
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.
 
 
NEXT ADVISORY
-------------
Next complete advisory at 1100 AM AST.
 
$$
Forecaster Reinhart
 

Hurricane Sam Forecast Advisory Number 23

Issued at 0900 UTC TUE SEP 28 2021  

000
WTNT23 KNHC 280841
TCMAT3
 
HURRICANE SAM FORECAST/ADVISORY NUMBER  23
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182021
0900 UTC TUE SEP 28 2021
 
THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.
 
HURRICANE CENTER LOCATED NEAR 17.2N  53.9W AT 28/0900Z
POSITION ACCURATE WITHIN  15 NM
 
PRESENT MOVEMENT TOWARD THE NORTHWEST OR 310 DEGREES AT   8 KT
 
ESTIMATED MINIMUM CENTRAL PRESSURE  953 MB
EYE DIAMETER  25 NM
MAX SUSTAINED WINDS 115 KT WITH GUSTS TO 140 KT.
64 KT....... 35NE  30SE  25SW  30NW.
50 KT....... 60NE  50SE  40SW  50NW.
34 KT.......110NE  90SE  70SW  90NW.
12 FT SEAS..120NE  90SE  90SW 120NW.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT.  RADII IN NAUTICAL
MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.
 
REPEAT...CENTER LOCATED NEAR 17.2N  53.9W AT 28/0900Z
AT 28/0600Z CENTER WAS LOCATED NEAR 17.0N  53.6W
 
FORECAST VALID 28/1800Z 17.9N  54.7W
MAX WIND 120 KT...GUSTS 145 KT.
64 KT... 35NE  30SE  25SW  30NW.
50 KT... 60NE  50SE  40SW  50NW.
34 KT...110NE 100SE  70SW  90NW.
 
FORECAST VALID 29/0600Z 18.8N  55.9W
MAX WIND 115 KT...GUSTS 140 KT.
64 KT... 35NE  30SE  25SW  30NW.
50 KT... 60NE  50SE  40SW  50NW.
34 KT...110NE 100SE  70SW  90NW.
 
FORECAST VALID 29/1800Z 19.9N  57.4W
MAX WIND 115 KT...GUSTS 140 KT.
64 KT... 40NE  35SE  25SW  35NW.
50 KT... 60NE  50SE  40SW  50NW.
34 KT...110NE 100SE  70SW  90NW.
 
FORECAST VALID 30/0600Z 21.3N  59.0W
MAX WIND 110 KT...GUSTS 135 KT.
64 KT... 45NE  40SE  30SW  40NW.
50 KT... 70NE  60SE  40SW  50NW.
34 KT...120NE 110SE  80SW 100NW.
 
FORECAST VALID 30/1800Z 23.2N  60.5W
MAX WIND 110 KT...GUSTS 135 KT.
50 KT... 70NE  60SE  50SW  60NW.
34 KT...120NE 120SE  90SW 100NW.
 
FORECAST VALID 01/0600Z 25.6N  61.5W
MAX WIND 110 KT...GUSTS 135 KT.
50 KT... 70NE  70SE  50SW  60NW.
34 KT...130NE 130SE  90SW 100NW.
 
EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 150 NM
ON DAY 4 AND 175 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY
 
OUTLOOK VALID 02/0600Z 31.4N  60.7W
MAX WIND 105 KT...GUSTS 130 KT.
 
OUTLOOK VALID 03/0600Z 39.0N  56.0W
MAX WIND  95 KT...GUSTS 115 KT.
 
REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 17.2N  53.9W
 
NEXT ADVISORY AT 28/1500Z
 
$$
FORECASTER REINHART
 
 

Hurricane Sam Forecast Discussion Number 23

Issued at 500 AM AST Tue Sep 28 2021  

053 
WTNT43 KNHC 280844
TCDAT3
 
Hurricane Sam Discussion Number  23
NWS National Hurricane Center Miami FL       AL182021
500 AM AST Tue Sep 28 2021
 
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.
 
 
Key Messages:
 
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.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/0900Z 17.2N  53.9W  115 KT 130 MPH
 12H  28/1800Z 17.9N  54.7W  120 KT 140 MPH
 24H  29/0600Z 18.8N  55.9W  115 KT 130 MPH
 36H  29/1800Z 19.9N  57.4W  115 KT 130 MPH
 48H  30/0600Z 21.3N  59.0W  110 KT 125 MPH
 60H  30/1800Z 23.2N  60.5W  110 KT 125 MPH
 72H  01/0600Z 25.6N  61.5W  110 KT 125 MPH
 96H  02/0600Z 31.4N  60.7W  105 KT 120 MPH
120H  03/0600Z 39.0N  56.0W   95 KT 110 MPH
 
$$
Forecaster Reinhart
 

Hurricane Sam Wind Speed Probabilities Number 23

Issued at 0900 UTC TUE SEP 28 2021


000
FONT13 KNHC 280842
PWSAT3
                                                                    
HURRICANE SAM WIND SPEED PROBABILITIES NUMBER  23                   
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182021               
0900 UTC TUE SEP 28 2021                                            
                                                                    
AT 0900Z THE CENTER OF HURRICANE SAM WAS LOCATED NEAR LATITUDE 17.2 
NORTH...LONGITUDE 53.9 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 115   
KTS...130 MPH...215 KM/H.                                           
                                                                    
Z INDICATES COORDINATED UNIVERSAL TIME (GREENWICH)                  
   ATLANTIC STANDARD TIME (AST)...SUBTRACT 4 HOURS FROM Z TIME      
   EASTERN  DAYLIGHT TIME (EDT)...SUBTRACT 4 HOURS FROM Z TIME      
   CENTRAL  DAYLIGHT TIME (CDT)...SUBTRACT 5 HOURS FROM Z TIME      
                                                                    
WIND SPEED PROBABILITY TABLE FOR SPECIFIC LOCATIONS                 
                                                                    
CHANCES OF SUSTAINED (1-MINUTE AVERAGE) WIND SPEEDS OF AT LEAST     
   ...34 KT (39 MPH... 63 KM/H)...                                  
   ...50 KT (58 MPH... 93 KM/H)...                                  
   ...64 KT (74 MPH...119 KM/H)...                                  
FOR LOCATIONS AND TIME PERIODS DURING THE NEXT 5 DAYS               
                                                                    
PROBABILITIES FOR LOCATIONS ARE GIVEN AS OP(CP) WHERE               
    OP  IS THE PROBABILITY OF THE EVENT BEGINNING DURING            
        AN INDIVIDUAL TIME PERIOD (ONSET PROBABILITY)               
   (CP) IS THE PROBABILITY OF THE EVENT OCCURRING BETWEEN           
        06Z TUE AND THE FORECAST HOUR (CUMULATIVE PROBABILITY)      
                                                                    
PROBABILITIES ARE GIVEN IN PERCENT                                  
X INDICATES PROBABILITIES LESS THAN 1 PERCENT                       
PROBABILITIES FOR 34 KT AND 50 KT ARE SHOWN AT A GIVEN LOCATION WHEN
THE 5-DAY CUMULATIVE PROBABILITY IS AT LEAST 3 PERCENT.             
PROBABILITIES FOR 34...50...64 KT SHOWN WHEN THE 5-DAY              
64-KT CUMULATIVE PROBABILITY IS AT LEAST 1 PERCENT.                 
                                                                    
                                                                    
  - - - - WIND SPEED PROBABILITIES FOR SELECTED LOCATIONS - - - -   
                                                                    
               FROM    FROM    FROM    FROM    FROM    FROM    FROM 
  TIME       06Z TUE 18Z TUE 06Z WED 18Z WED 06Z THU 06Z FRI 06Z SAT
PERIODS         TO      TO      TO      TO      TO      TO      TO  
             18Z TUE 06Z WED 18Z WED 06Z THU 06Z FRI 06Z SAT 06Z SUN
                                                                    
FORECAST HOUR    (12)   (24)    (36)    (48)    (72)    (96)   (120)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
LOCATION       KT                                                   
                                                                    
CAPE RACE NFLD 34  X   X( X)   X( X)   X( X)   X( X)   X( X)   3( 3)
 
SABLE ISLAND   34  X   X( X)   X( X)   X( X)   X( X)   X( X)   6( 6)
 
BERMUDA        34  X   X( X)   X( X)   X( X)   1( 1)  19(20)   3(23)
BERMUDA        50  X   X( X)   X( X)   X( X)   X( X)   7( 7)   1( 8)
BERMUDA        64  X   X( X)   X( X)   X( X)   X( X)   3( 3)   1( 4)
 
SAINT MAARTEN  34  X   X( X)   1( 1)   1( 2)   1( 3)   X( 3)   X( 3)
 
ST EUSTATIUS   34  X   X( X)   1( 1)   1( 2)   X( 2)   1( 3)   X( 3)
 
ST KITTS-NEVIS 34  X   X( X)   1( 1)   1( 2)   X( 2)   1( 3)   X( 3)
 
BARBUDA        34  X   X( X)   2( 2)   2( 4)   1( 5)   1( 6)   X( 6)
 
ANTIGUA        34  X   X( X)   2( 2)   1( 3)   1( 4)   X( 4)   X( 4)
 
$$                                                                  
FORECASTER REINHART                                                 

Hurricane Sam Graphics


Hurricane Sam 5-Day Uncertainty Track Image
5-Day Uncertainty Track last updated Tue, 28 Sep 2021 08:46:55 GMT

Hurricane Sam 34-Knot Wind Speed Probabilities
Wind Speed Probabilities last updated Tue, 28 Sep 2021 09:22:55 GMT