171
AXNT20 KNHC 211339 AAA
TWDAT
TROPICAL WEATHER DISCUSSION...UPDATED
NWS NATIONAL HURRICANE CENTER MIAMI FL
939 AM EDT FRI SEP 21 2018
UPDATED CARIBBEAN SEA SECTION
TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA, CENTRAL AMERICA
GULF OF MEXICO, CARIBBEAN SEA, NORTHERN SECTIONS OF SOUTH
AMERICA, AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE
EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE
IMAGERY, WEATHER OBSERVATIONS, RADAR AND METEOROLOGICAL ANALYSIS.
BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1300 UTC.
..TROPICAL WAVES
A TROPICAL WAVE IS LIKELY TO BE ANALYZED TODAY NEAR THE COAST OF
AFRICA BASED ON MODEL GUIDANCE AND SATELLITE IMAGERY. PRESENTLY,
SATELLITE IMAGERY SHOWS A BROAD CANOPY OF MULTILAYER CLOUDS WITH
SCATTERED MODERATE TO STRONG CONVECTION AHEAD OF THE WAVE FROM
04N TO 13N BETWEEN 16W AND 21W. THE IMAGERY ALSO SHOWS PRETTY
GOOD UPPER-LEVEL OUTFLOW WITH THIS ACTIVITY DENOTED BY THE
CIRRUS CLOUDS FANNING OUTWARD FROM THE CONVECTION.
A FAR EASTERN ATLANTIC OCEAN HAS ITS AXIS ALONG 26W/27W FROM 03N
TO 20N, MOVING WESTWARD AT 10 TO 15 KT. ONLY ISOLATED SHOWERS
AND WEAK THUNDERSTORMS ARE WITHIN 60 NM EITHER SIDE OF THE WAVE
AXIS FROM 04N TO 08N.
A CENTRAL ATLANTIC TROPICAL WAVE HAS ITS AXIS ALONG 51W FROM 05N
TO 19N, MOVING WESTWARD AT 10 TO 15 KT. THIS FEATURE WAS
ANALYZED AS A LOW 24 HOURS, BUT DURING THE PAST 12 HOURS
WEAKENED TO WAVE. THE FIRST VISIBLE IMAGES SHOW A CLEARLY
EXPOSED LOW-LEVEL CENTER MOVING WESTWARD AT 13N52W. THE IMAGERY
SHOWS SCATTERED MODERATE TO ISOLATED STRONG CONVECTION WITHIN 60
NM EITHER SIDE OF THE WAVE FROM 11N TO 14N. SCATTERED MODERATE
CONVECTION IS WITHIN 30 NM OF 12N48W AND WITHIN 30 NM OF 11N49W.
ISOLATED SHOWERS ARE WITHIN 30 NM OF THE EXPOSED LOW. DRY MID-
LEVEL AIR AND STRONG UPPER-LEVEL WINDS ARE EXPECTED TO HINDER
ANY DEVELOPMENT OF THIS DISTURBANCE WHILE IT MOVES TOWARD THE
WNW.
A CENTRAL CARIBBEAN SEA TROPICAL WAVE HAS ITS AXIS ALONG 74W SOUTH
OF 20N, MOVING WESTWARD AT 10 TO 15 KT. SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS ARE SEEN WITHIN 240 NM EAST OF THE WAVE
AXIS NORTH OF 15N TO ACROSS THE DOMINICAN REPUBLIC. ISOLATED
SHOWERS AND THUNDERSTORMS ARE NORTH OF 15N AND WEST OF THE WAVE
TO 75W. SATELLITE IMAGERY IS DEPICTING SAHARAN DUST TO THE EAST
OF THE WAVE OVER MUCH OF THE EASTERN CARIBBEAN, AND EAST FROM
THERE TO OVER THE TROPICAL ATLANTIC WATERS. SURFACE OBSERVATIONS
FROM PUERTO RICO AND THE U.S. VIRGIN ISLANDS INDICATE
VISIBILITIES OF 6 SM IN HAZE.
..MONSOON TROUGH/ITCZ
THE MONSOON TROUGH AXIS EXTENDS FROM THE COASTAL BORDER SECTIONS
OF GUINEA AND SIERRA LEONE NEAR NEW TO 05N20W. THE ITCZ
CONTINUES FROM 05N20W TO 06N28W, TO 05N38W, AND 08N44W. OTHER THAN
CONVECTION ASSOCIATED WITH THE WAVE ALONG THE COAST OF AFRICA,
AND WITH THE ONE ALONG 26W/27W, SCATTERED MODERATE CONVECTION IS
SEEN WITHIN 210 NM NORTH OF THE ITCZ BETWEEN 40W AND 45W.
..DISCUSSION
GULF OF MEXICO...
AN UPPER-LEVEL CYCLONIC CIRCULATION CENTER IS MOVING WESTWARD
OVER S FLORIDA NEAR 26N81W. THE LOW EXTENDS A TROUGH SOUTHWARD
TO ACROSS CENTRAL CUBA AND TO THE WESTERN CARIBBEAN SEA.
ASSOCIATED UPPER-LEVEL CYCLONIC WIND FLOW COVERS FLORIDA, THE
GULF OF MEXICO, AND THE ATLANTIC OCEAN FROM THE FLORIDA STRAITS
TO 32N BETWEEN 75W AND 85W. SCATTERED SHOWERS AND THUNDERSTORMS
ARE OVER THE EASTERN GULF WATERS FROM 24N TO 27N EAST OF 85W.
ISOLATED SHOWERS AND THUNDERSTORMS ARE ELSEWHERE OVER THE BASIN.
HIGH PRESSURE BUILDING IN THE EASTERN U.S.A. WILL SUPPORT GENTLE
TO MODERATE E TO SE WINDS, AND SEA HEIGHTS RANGING FROM 1 FOOT TO
4 FEET, ACROSS THE BASIN THROUGH SUN. IT IS POSSIBLE THAT TYPICAL
NOCTURNAL SURFACE TROUGH, THAT WILL BE MOVING WESTWARD ACROSS THE
SOUTHWESTERN CORNER OF THE GULF OF MEXICO, MAY PRODUCE LOCALLY
FRESH WINDS THROUGH SAT
CARIBBEAN SEA...UPDATED
BROAD UPPER-LEVEL CYCLONIC FLOW IS PRESENT OVER THE WESTERN
SECTION OF THE SEA NORTH OF 15N AND WEST OF 78W IN ASSOCIATION
WITH THE UPPER TROUGH THAT EXTENDS FROM THE UPPER LOW OVER S
FLORIDA TO A BASE NEAR 16N82W. SCATTERED SHOWERS AND
THUNDERSTORMS FROM 14N TO 19N WEST OF 75W ARE INCREASING IN
COVERAGE AS THE UPPER TROUGH ACTING ON A VERY UNSTABLE
ATMOSPHERE IS RESULTING IN AMPLE INSTABILITY THERE.
A PATCH OF LOW-LEVEL MOISTURE ADVECTING WESTWARD OVER THE
NORTHEASTERN CARIBBEAN IS ACCOMPANIED BY SCATTERED SHOWERS.
THESE SHOWERS SHOULD CONTINUE OVER THE SECTION OF THE CARIBBEAN
INTO MOST OF THIS AFTERNOON.
THE EASTERN PACIFIC MONSOON TROUGH AXIS EXTENDS ACROSS COSTA
RICA TO ALONG 09N AND TO NORTHWESTERN COLOMBIA NEAR 75W. THIS
ALONG WITH LOW-LEVEL WIND SPEED CONVERGENCE IS LEADING TO
SCATTERED MODERATE TO STRONG CONVECTION OVER THE FAR WESTERN
PORTION OF THE SOUTHWESTERN CARIBBEAN SOUTH OF 14N AND WEST OF
80W. ISOLATED SHOWERS AND THUNDERSTORMS ARE ELSEWHERE WEST OF
70W.
THE CENTRAL CARIBBEAN TROPICAL WAVE WILL MOVE WESTWARD INTO
CENTRAL AMERICA THROUGH SUN. THE PRESSURE GRADIENT BETWEEN
CENTRAL ATLANTIC HIGH PRESSURE AND THE LOWER PRESSURE NEAR THE
WAVE WILL SUPPORT MODERATE TO FRESH TRADES TODAY. TRADES WILL
DIMINISH OVER MUCH OF THE BASIN THIS WEEKEND.
ATLANTIC OCEAN...
AN UPPER-LEVEL CYCLONIC CIRCULATION CENTER IS NEAR 28N80W, MOVING
FROM THE ATLANTIC OCEAN TOWARD FLORIDA. UPPER LEVEL CYCLONIC WIND
FLOW COVERS FLORIDA, THE GULF OF MEXICO, AND THE ATLANTIC OCEAN
FROM THE FLORIDA STRAITS TO 32N BETWEEN 75W AND 85W. ISOLATED
MODERATE RAINSHOWERS ARE IN THE AREA OF UPPER LEVEL CYCLONIC WIND
FLOW. OTHER ISOLATED MODERATE RAINSHOWERS ARE IN THE ATLANTIC
OCEAN FROM 25N TO 30N BETWEEN 70W AND 75W.
A 1008 MB LOW IS JUST NORTH OF THE AREA AT 33N63W, WITH A RATHER
WEAK COLD FRONT EXTENDING TO 28N70W AND TO 29N80W. THE LOW HAS
SIGNIFICANTLY WEAKEN SINCE YESTERDAY. THE COMBINATION OF DRY AIR
AND STRONG UPPER-LEVEL WINDS IS EXPECTED TO INHIBIT ANY
SIGNIFICANT DEVELOPMENT OF THIS LOW FOR THE NEXT SEVERAL DAYS
WHILE IT MOVES SOUTHWARD TODAY, AND THEN DRIFTS WESTWARD TO THE
SOUTHWEST OF BERMUDA SAT THROUGH SUN. SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS ARE SEEN WITHIN 90 NM SOUTH OF THE FRONT
WEST OF 77W.
A SURFACE TROUGH EXTENDS FROM NEAR 32N34W TO A 1017 MB LOW,
REMNANTS OF FORMER TROPICAL CYCLONE JOYCE, AT 30.5N35W AND TO
NEAR 24N36W. ISOLATED SHOWERS AND THUNDERSTORMS ARE WITHIN 30 NM
OF THE LOW.
AN UPPER-LEVEL TROUGH EXTENDS FROM AN UPPER-LEVEL LOW AT 31N24W
TO 29N30W, WHERE IT BECOMES A CYCLONIC SHEAR AXIS TO ANOTHER
UPPER-LEVEL LOW NEAR 29N41W. A TROUGH EXTENDS FROM THIS LOW TO
22N45W TO 17N52W AND TO A BASE AT 10N58W. SCATTERED MODERATE
CONVECTION IS WITHIN 30 NM EITHER SIDE OF A LINE FROM 28N42W TO
29N39W. ISOLATED SHOWERS ARE SEEN FROM NEAR 20N TO 28N BETWEEN
40W AND 50W.
THE AFOREMENTIONED COLD FRONT IS FORECAST TO DRIFT SLIGHTLY
SOUTHWARD TODAY, THEN DISSIPATE BY EARLY ON SAT. THE 1017 MB OW
WILL MEANDER ACROSS IN A CLOCKWISE MOTION THROUGH EARLY NEXT
WEEK. NE SWELL IS FORECAST TO AFFECT THE WATERS E OF THE BAHAMAS
THROUGH EARLY NEXT WEEK.
FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE
AGUIRRE
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