Atlantic Tropical Weather Outlook

000
ABNT20 KNHC 272342
TWOAT 

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 PM EDT Mon Sep 27 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 well-defined low pressure system associated with the remnants of 
Peter is located a few hundred miles east of Bermuda. Although 
shower and thunderstorm activity is currently disorganized, 
environmental conditions are expected to remain marginally 
conducive for a short-lived tropical depression to form tonight or 
Tuesday while the system moves northeastward at about 10 mph.  By 
Wednesday, however, conditions are expected to become unfavorable 
for further development.
* Formation chance through 48 hours...medium...60 percent.
* Formation chance through 5 days...medium...60 percent.

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 just offshore the west coast of Africa 
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 couple 
of days 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.

$$
Forecaster Stewart

Summary for Hurricane Sam (AT3/AL182021)

...SAM EXPECTED TO REMAIN A POWERFUL HURRICANE FOR SEVERAL MORE  DAYS...
 As of 11:00 PM AST Mon Sep 27
 the center of Sam was located near 16.8, -53.2
 with movement NW at 9 mph.
 The minimum central pressure was 956 mb
 with maximum sustained winds of about 120 mph.

Hurricane Sam Public Advisory Number 22

Issued at 1100 PM AST Mon Sep 27 2021  

000
WTNT33 KNHC 280232
TCPAT3
 
BULLETIN
Hurricane Sam Advisory Number  22
NWS National Hurricane Center Miami FL       AL182021
1100 PM AST Mon Sep 27 2021
 
...SAM EXPECTED TO REMAIN A POWERFUL HURRICANE FOR SEVERAL MORE 
DAYS...
 
 
SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...16.8N 53.2W
ABOUT 660 MI...1060 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...120 MPH...195 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 9 MPH...15 KM/H
MINIMUM CENTRAL PRESSURE...956 MB...28.23 INCHES
 
 
WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.
 
 
DISCUSSION AND OUTLOOK
----------------------
At 1100 PM AST (0300 UTC), the center of Hurricane Sam was located
near latitude 16.8 North, longitude 53.2 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 to the north is expected by Friday.
On the forecast track, Sam will pass well to the northeast of the
northern Leeward Islands Wednesday and Thursday.
 
Data from a NOAA Hurricane Hunter plane indicate that maximum 
sustained winds remain near 120 mph (195 km/h) with higher gusts.  
Sam is a category 3 hurricane on the Saffir-Simpson Hurricane Wind 
Scale.  The hurricane could strengthen some overnight, and Sam is 
anticipated to be a category 3 or 4 hurricane for the next several 
days.
 
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 from NOAA aircraft data is 
956 mb (28.23 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 mid-to-late week, 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 500 AM AST.
 
$$
Forecaster Blake

Hurricane Sam Forecast Advisory Number 22

Issued at 0300 UTC TUE SEP 28 2021  

000
WTNT23 KNHC 280232
TCMAT3
 
HURRICANE SAM FORECAST/ADVISORY NUMBER  22
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182021
0300 UTC TUE SEP 28 2021
 
THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.
 
HURRICANE CENTER LOCATED NEAR 16.8N  53.2W AT 28/0300Z
POSITION ACCURATE WITHIN  15 NM
 
PRESENT MOVEMENT TOWARD THE NORTHWEST OR 315 DEGREES AT   8 KT
 
ESTIMATED MINIMUM CENTRAL PRESSURE  956 MB
MAX SUSTAINED WINDS 105 KT WITH GUSTS TO 130 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 16.8N  53.2W AT 28/0300Z
AT 28/0000Z CENTER WAS LOCATED NEAR 16.5N  52.9W
 
FORECAST VALID 28/1200Z 17.5N  54.0W
MAX WIND 115 KT...GUSTS 140 KT.
64 KT... 35NE  30SE  25SW  30NW.
50 KT... 60NE  50SE  40SW  50NW.
34 KT...110NE  90SE  70SW  90NW.
 
FORECAST VALID 29/0000Z 18.4N  55.1W
MAX WIND 115 KT...GUSTS 140 KT.
64 KT... 35NE  30SE  25SW  30NW.
50 KT... 60NE  50SE  40SW  50NW.
34 KT...110NE  90SE  70SW  90NW.
 
FORECAST VALID 29/1200Z 19.3N  56.4W
MAX WIND 110 KT...GUSTS 135 KT.
64 KT... 40NE  30SE  25SW  30NW.
50 KT... 60NE  50SE  40SW  50NW.
34 KT...110NE  90SE  70SW  90NW.
 
FORECAST VALID 30/0000Z 20.6N  58.0W
MAX WIND 110 KT...GUSTS 135 KT.
64 KT... 45NE  40SE  30SW  40NW.
50 KT... 70NE  60SE  40SW  50NW.
34 KT...120NE 100SE  70SW 100NW.
 
FORECAST VALID 30/1200Z 22.2N  59.7W
MAX WIND 110 KT...GUSTS 135 KT.
50 KT... 70NE  60SE  40SW  50NW.
34 KT...120NE 100SE  70SW 100NW.
 
FORECAST VALID 01/0000Z 24.3N  61.0W
MAX WIND 110 KT...GUSTS 135 KT.
50 KT... 70NE  60SE  50SW  60NW.
34 KT...130NE 110SE  80SW 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 02/0000Z 29.6N  61.5W
MAX WIND 105 KT...GUSTS 130 KT.
 
OUTLOOK VALID 03/0000Z 37.5N  56.9W
MAX WIND 100 KT...GUSTS 120 KT.
 
REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 16.8N  53.2W
 
NEXT ADVISORY AT 28/0900Z
 
$$
FORECASTER BLAKE

Hurricane Sam Forecast Discussion Number 22

Issued at 1100 PM AST Mon Sep 27 2021  

000
WTNT43 KNHC 280234
TCDAT3
 
Hurricane Sam Discussion Number  22
NWS National Hurricane Center Miami FL       AL182021
1100 PM AST Mon Sep 27 2021
 
The NOAA Hurricane Hunters have been flying through Sam tonight, 
with radar and wind observations showing broken concentric eyewalls 
at times.  The maximum 700-mb flight-level winds on the mission 
were 114 kt, with peak SFMR values to 103 kt and a central pressure 
around 956 mb, so the initial wind speed will remain 105 kt.  While 
the overall intensity doesn't seem to have changed much in the past 
several hours, the aircraft data show that the hurricane has grown 
in size, and that is reflected in the initial wind radii.

The future intensity of Sam is hard to pinpoint.  Eyewall cycles 
will likely play a key role in determining its second peak intensity 
since the hurricane should remain in low- or moderate-shear and 
warm-water environments for the next few days.  Those cycles are 
basically impossible to forecast, but there is some suggestion on 
satellite that a larger eye is trying to form, which could allow for 
some increase in strength in the near term.  It seems likely that 
Sam will be a category 3 or 4 hurricane given the conducive 
environment for most of the forecast period, so the new NHC forecast 
is similar to the previous one, with the most significant change 
showing a larger hurricane consistent with the latest guidance.  

Sam continues to move northwestward, or 315/8 kt.  The hurricane 
should move in that direction for the next few days around the 
southwestern portion of the subtropical high.  A turn to the north 
is likely as Sam meets the western edge of the high, with a gradual 
acceleration to the northeast anticipated by the weekend due to an 
incoming mid-latitude trough from the west.  While there are some 
speed differences in the models, especially near and after 
recurvature, the NHC forecast leans toward the faster GFS solution 
over the slower ECMWF, given the magnitude of the strong 
southwesterly flow that Sam should encounter at long range, plus a 
nod to the superior performance of late for the American model.  The 
new forecast is adjusted a bit to the right and faster beyond day 3, 
with no significant changes made before that time.

 
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  28/0300Z 16.8N  53.2W  105 KT 120 MPH
 12H  28/1200Z 17.5N  54.0W  115 KT 130 MPH
 24H  29/0000Z 18.4N  55.1W  115 KT 130 MPH
 36H  29/1200Z 19.3N  56.4W  110 KT 125 MPH
 48H  30/0000Z 20.6N  58.0W  110 KT 125 MPH
 60H  30/1200Z 22.2N  59.7W  110 KT 125 MPH
 72H  01/0000Z 24.3N  61.0W  110 KT 125 MPH
 96H  02/0000Z 29.6N  61.5W  105 KT 120 MPH
120H  03/0000Z 37.5N  56.9W  100 KT 115 MPH
 
$$
Forecaster Blake

Hurricane Sam Wind Speed Probabilities Number 22

Issued at 0300 UTC TUE SEP 28 2021                                              

000
FONT13 KNHC 280233
PWSAT3
                                                                    
HURRICANE SAM WIND SPEED PROBABILITIES NUMBER  22                   
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182021               
0300 UTC TUE SEP 28 2021                                            
                                                                    
AT 0300Z THE CENTER OF HURRICANE SAM WAS LOCATED NEAR LATITUDE 16.8 
NORTH...LONGITUDE 53.2 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 105   
KTS...120 MPH...195 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           
        00Z 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       00Z TUE 12Z TUE 00Z WED 12Z WED 00Z THU 00Z FRI 00Z SAT
PERIODS         TO      TO      TO      TO      TO      TO      TO  
             12Z TUE 00Z WED 12Z WED 00Z THU 00Z FRI 00Z SAT 00Z SUN
                                                                    
FORECAST HOUR    (12)   (24)    (36)    (48)    (72)    (96)   (120)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
LOCATION       KT                                                   
                                                                    
SABLE ISLAND   34  X   X( X)   X( X)   X( X)   X( X)   X( X)   3( 3)
 
BERMUDA        34  X   X( X)   X( X)   X( X)   X( X)  14(14)   9(23)
BERMUDA        50  X   X( X)   X( X)   X( X)   X( X)   4( 4)   3( 7)
BERMUDA        64  X   X( X)   X( X)   X( X)   X( X)   2( 2)   2( 4)
 
SAINT MAARTEN  34  X   X( X)   X( X)   1( 1)   2( 3)   X( 3)   X( 3)
 
BARBUDA        34  X   X( X)   1( 1)   2( 3)   3( 6)   X( 6)   X( 6)
 
ANTIGUA        34  X   X( X)   1( 1)   1( 2)   2( 4)   X( 4)   X( 4)
 
$$                                                                  
FORECASTER BLAKE

Hurricane Sam Graphics

5-Day Uncertainty Track last updated Tue, 28 Sep 2021 02:34:53 GMT


Wind Speed Probabilities last updated Tue, 28 Sep 2021 03:22:57 GMT