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Atlantic Tropical Weather Outlook



000

ABNT20 KNHC 240534

TWOAT 



Tropical Weather Outlook

NWS National Hurricane Center Miami FL

200 AM EDT Fri Sep 24 2021



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



The National Hurricane Center is issuing advisories on Tropical 

Storm Sam, located about 1500 miles east-southeast of the northern 

Leeward Islands.



A gale-force, non-tropical low pressure system, the remnants of 

Odette, is located a little more than 600 miles west-northwest of 

the westernmost Azores.  Showers and thunderstorms remain limited 

near the low, and this system has only a brief window of opportunity 

to become a subtropical or tropical cyclone while it moves generally 

south-southeastward over marginally warmer waters.  Strong 

upper-level winds are expected to develop over the system by late 

today, which should then limit further development.  Additional 

information on this system, including gale warnings, can be found in 

High Seas Forecasts issued by the National Weather Service.

* Formation chance through 48 hours...medium...40 percent.

* Formation chance through 5 days...medium...40 percent.



A large area of showers and thunderstorms centered a couple of 

hundred miles east of Bermuda is associated with a surface and 

upper-level trough.  Some tropical or subtropical development 

of this system could occur through early Saturday as it moves 

generally north-northwestward.  After that time, development 

is not expected due to strong upper-level winds. 

* Formation chance through 48 hours...low...20 percent.

* Formation chance through 5 days...low...20 percent.



A tropical wave is expected to move off the west coast of Africa by 

the end of this weekend.  Thereafter, environmental conditions are 

forecast to be conducive for gradual development, and a tropical 

depression could form by the middle of next week while the system 

moves westward at 10 to 15 mph over the far eastern tropical 

Atlantic.

* Formation chance through 48 hours...low...near 0 percent.

* Formation chance through 5 days...medium...40 percent.



&&



High Seas Forecasts issued by the National Weather Service can be 

found under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and 

online at ocean.weather.gov/shtml/NFDHSFAT1.php



$$

Forecaster Cangialosi

Summary for Hurricane Sam (AT3/AL182021)

...SAM IS NOW A HURRICANE... ...RAPID INTENSIFICATION FORECAST TO CONTINUE...
 As of 5:00 AM AST Fri Sep 24
 the center of Sam was located near 11.5, -42.2
 with movement W at 15 mph.
 The minimum central pressure was 993 mb
 with maximum sustained winds of about 75 mph.

Hurricane Sam Public Advisory Number 7

Issued at 500 AM AST Fri Sep 24 2021  
000
WTNT33 KNHC 240831
TCPAT3
 
BULLETIN
Hurricane Sam Advisory Number   7
NWS National Hurricane Center Miami FL       AL182021
500 AM AST Fri Sep 24 2021
 
...SAM IS NOW A HURRICANE...
...RAPID INTENSIFICATION FORECAST TO CONTINUE...
 
 
SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...11.5N 42.2W
ABOUT 1470 MI...2365 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...75 MPH...120 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...993 MB...29.33 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 11.5 North, longitude 42.2 West. Sam is moving toward 
the west near 15 mph (24 km/h) and this motion is expected to 
continue through tonight.  A decrease in forward speed and a motion 
toward the west-northwest are expected over the weekend.

Maximum sustained winds have increased to near 75 mph (120 km/h) 
with higher gusts. Rapid intensification is forecast to continue, 
and Sam is likely to become a major hurricane tonight or early 
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 993 mb (29.33 inches).
 
 
HAZARDS AFFECTING LAND
----------------------
None.
 
 
NEXT ADVISORY
-------------
Next complete advisory at 1100 AM AST.
 
$$
Forecaster Cangialosi

Hurricane Sam Forecast Advisory Number 7

Issued at 0900 UTC FRI SEP 24 2021  
000
WTNT23 KNHC 240830
TCMAT3
 
HURRICANE SAM FORECAST/ADVISORY NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182021
0900 UTC FRI SEP 24 2021
 
THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.
 
HURRICANE CENTER LOCATED NEAR 11.5N  42.2W AT 24/0900Z
POSITION ACCURATE WITHIN  15 NM
 
PRESENT MOVEMENT TOWARD THE WEST OR 280 DEGREES AT  13 KT
 
ESTIMATED MINIMUM CENTRAL PRESSURE  993 MB
MAX SUSTAINED WINDS  65 KT WITH GUSTS TO  80 KT.
64 KT....... 15NE   0SE   0SW   0NW.
50 KT....... 30NE  20SE  15SW  20NW.
34 KT....... 50NE  40SE  30SW  40NW.
12 FT SEAS.. 90NE  30SE  30SW  60NW.
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 11.5N  42.2W AT 24/0900Z
AT 24/0600Z CENTER WAS LOCATED NEAR 11.4N  41.6W
 
FORECAST VALID 24/1800Z 11.7N  44.0W
MAX WIND  80 KT...GUSTS 100 KT.
64 KT... 15NE  10SE   0SW  10NW.
50 KT... 30NE  20SE  20SW  20NW.
34 KT... 70NE  50SE  30SW  50NW.
 
FORECAST VALID 25/0600Z 12.1N  45.9W
MAX WIND  95 KT...GUSTS 115 KT.
64 KT... 20NE  15SE  10SW  15NW.
50 KT... 30NE  30SE  20SW  30NW.
34 KT... 70NE  50SE  40SW  50NW.
 
FORECAST VALID 25/1800Z 12.5N  47.4W
MAX WIND 105 KT...GUSTS 130 KT.
64 KT... 20NE  15SE  10SW  15NW.
50 KT... 40NE  30SE  20SW  30NW.
34 KT... 80NE  60SE  40SW  60NW.
 
FORECAST VALID 26/0600Z 12.9N  48.7W
MAX WIND 115 KT...GUSTS 140 KT.
64 KT... 20NE  20SE  15SW  20NW.
50 KT... 40NE  30SE  30SW  30NW.
34 KT... 80NE  70SE  50SW  70NW.
 
FORECAST VALID 26/1800Z 13.4N  50.0W
MAX WIND 115 KT...GUSTS 140 KT.
50 KT... 50NE  40SE  30SW  40NW.
34 KT... 90NE  80SE  60SW  70NW.
 
FORECAST VALID 27/0600Z 14.1N  51.1W
MAX WIND 110 KT...GUSTS 135 KT.
50 KT... 50NE  40SE  30SW  40NW.
34 KT...100NE  80SE  60SW  80NW.
 
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 28/0600Z 15.9N  53.8W
MAX WIND 110 KT...GUSTS 135 KT.
 
OUTLOOK VALID 29/0600Z 17.8N  56.6W
MAX WIND 110 KT...GUSTS 135 KT.
 
REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 11.5N  42.2W
 
NEXT ADVISORY AT 24/1500Z
 
$$
FORECASTER CANGIALOSI

Hurricane Sam Forecast Discussion Number 7

Issued at 500 AM AST Fri Sep 24 2021  
000
WTNT43 KNHC 240831
TCDAT3
 
Hurricane Sam Discussion Number   7
NWS National Hurricane Center Miami FL       AL182021
500 AM AST Fri Sep 24 2021
 
Sam continues to rapidly intensify.  Satellite images show a small,
but well-developed inner core and pronounced curved bands that wrap
most of the way around the center.  There are some dry slots,
however, between the core and bands.  The latest satellite intensity
estimates range from 55 to 77 kt, and based on that data and the
continued improvement in the cyclone's structure, the initial wind
speed is increased to 65 kt.  This makes Sam a hurricane, the
seventh one of the 2021 Atlantic hurricane season. It should be
noted that Sam has a compact wind field, with hurricane-force and
tropical-storm-force winds estimated to only extend outward up to 15
and 50 n mi from the center, respectively.
 
Sam is moving westward at about 13 kt, and this general motion
should continue for another 12 to 24 hours as it moves in the flow
on the south side of a mid-level ridge.  After that time, a decrease
in forward speed and a turn to the west-northwest are expected, and
the official forecast has Sam moving at a slow pace of only 6-8 kt
during the 48-96-hour time period.  By the middle of next week, the
ridge is forecast to slide eastward as a trough moves over the
western Atlantic. In response, the hurricane will likely turn
northwestward as it approaches the northern Leeward Islands.  The
models have changed little this cycle with the GFS still on the
northern side of the guidance envelope and the ECMWF on the
southern side.  The NHC track forecast is essentially an update of
the previous one and lies between the GFS and ECMWF models, and near
the consensus aids.
 
The large scale environmental conditions all appear favorable for 
continued rapid intensification during the next day or so as the 
hurricane is expected to remain over warm 29 deg C waters and in 
very low wind shear conditions.  All of the SHIPS rapid 
intensification indices are well above the climatological means, and 
the NHC intensity forecast calls for Sam to become a major hurricane 
by early Saturday.  Beyond a couple of days, the environment is 
likely to become a little less ideal, and most of the models show 
Sam leveling off in strength, and so does the official forecast. 
This intensity prediction lies near a blend of the FSSE, HCCA, and 
IVCN consensus models.  Regardless of the details, Sam is expected 
to be a significant hurricane during the next several days.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/0900Z 11.5N  42.2W   65 KT  75 MPH
 12H  24/1800Z 11.7N  44.0W   80 KT  90 MPH
 24H  25/0600Z 12.1N  45.9W   95 KT 110 MPH
 36H  25/1800Z 12.5N  47.4W  105 KT 120 MPH
 48H  26/0600Z 12.9N  48.7W  115 KT 130 MPH
 60H  26/1800Z 13.4N  50.0W  115 KT 130 MPH
 72H  27/0600Z 14.1N  51.1W  110 KT 125 MPH
 96H  28/0600Z 15.9N  53.8W  110 KT 125 MPH
120H  29/0600Z 17.8N  56.6W  110 KT 125 MPH
 
$$
Forecaster Cangialosi

Hurricane Sam Wind Speed Probabilities Number 7

Issued at 0900 UTC FRI SEP 24 2021


000
FONT13 KNHC 240831
PWSAT3
                                                                    
HURRICANE SAM WIND SPEED PROBABILITIES NUMBER   7                   
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182021               
0900 UTC FRI SEP 24 2021                                            
                                                                    
AT 0900Z THE CENTER OF HURRICANE SAM WAS LOCATED NEAR LATITUDE 11.5 
NORTH...LONGITUDE 42.2 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 65 KTS
...75 MPH...120 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 FRI 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 FRI 18Z FRI 06Z SAT 18Z SAT 06Z SUN 06Z MON 06Z TUE
PERIODS         TO      TO      TO      TO      TO      TO      TO  
             18Z FRI 06Z SAT 18Z SAT 06Z SUN 06Z MON 06Z TUE 06Z WED
                                                                    
FORECAST HOUR    (12)   (24)    (36)    (48)    (72)    (96)   (120)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
LOCATION       KT                                                   
                                                                    
SAINT MAARTEN  34  X   X( X)   X( X)   X( X)   X( X)   X( X)   4( 4)
 
SABA           34  X   X( X)   X( X)   X( X)   X( X)   X( X)   3( 3)
 
ST EUSTATIUS   34  X   X( X)   X( X)   X( X)   X( X)   X( X)   5( 5)
 
ST KITTS-NEVIS 34  X   X( X)   X( X)   X( X)   X( X)   X( X)   5( 5)
 
BARBUDA        34  X   X( X)   X( X)   X( X)   X( X)   X( X)   8( 8)
 
ANTIGUA        34  X   X( X)   X( X)   X( X)   X( X)   1( 1)   6( 7)
 
GUADELOUPE     34  X   X( X)   X( X)   X( X)   X( X)   1( 1)   6( 7)
 
DOMINICA       34  X   X( X)   X( X)   X( X)   X( X)   X( X)   6( 6)
 
MARTINIQUE     34  X   X( X)   X( X)   X( X)   X( X)   1( 1)   5( 6)
 
SAINT LUCIA    34  X   X( X)   X( X)   X( X)   X( X)   X( X)   3( 3)
 
BARBADOS       34  X   X( X)   X( X)   X( X)   X( X)   2( 2)   3( 5)
 
$$                                                                  
FORECASTER CANGIALOSI

Hurricane Sam Graphics




5-Day Uncertainty Track last updated Fri, 24 Sep 2021 08:33:27 GMT



 

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