Prognostic Meteorological Discussion
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FXCA20 KWBC 191818
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
217 PM EDT THU OCT 19 2017

TROPICAL DISCUSSION FROM OCT 19/12 UTC: STRONG POLAR EXITING THE
EAST COAST OF THE UNITED STATES IS INTERACTING WITH A SURFACE
FRONT THAT LIES ACROSS THE BAHAMAS. THE UPPER TROUGH IS STARTING
TO UNDULATE A SURFACE LOW NEAR 30N 70W...AND TO PUSH THE FRONT
SOUTHWARD. ALTHOUGH THERE IS NO STRONG BAROCLINICITY WITH THIS
SYSTEM...THE FRONT IS FORECAST TO ENHANCE CONVECTION AS IT
PROPAGATES TO THE SOUTH. BY THURSDAY EVENING...THE FRONT IS
FORECAST TO MEANDER JUST TO THE NORTH OF GRAND BAHAMA TO THEN
BECOME STATIONARY. A POOL OF MOISTURE WITH PRECIPITABLE WATER
VALUES EXCEEDING 50MM IS FAVORING SCATTERED CONVECTION. THIS
ACTIVITY WILL AFFECT THE BAHAMAS DURING THE NEXT THREE DAYS.
RAINFALL ACCUMULATIONS ARE FORECAST TO GRADUALLY DECREASE FROM
10-15MM/DAY AND MAXIMA OF 20-35MM ON THURSDAY TO 05-10MM/DAY AND
MAXIMA OF 15MM BY SATURDAY.

TO THE WEST...WANING NORTHERLY WIND SURGE IN THE GULF OF
MEXICO/GULF OF HONDURAS IS STILL SUSTAINING ENHANCED MOISTURE
CONVERGENCE AGAINST THE NORTHERN SLOPES OF NORTHERN CENTRAL
AMERICA. ALTHOUGH THE SURGE CONTINUES WANING...A TROPICAL WAVE IS
APPROACHING FROM THE EAST...AND WILL REINFORCE CURRENT MOIST
PATTERN IN THE REGION. REGARDLESS...PRECIPITABLE WATER VALUES IN
THE GULF OF HONDURAS ARE EXCEEDING 55MM. THIS WILL CONTINUE
FAVORING MODERATE PRECIPITATION. THROUGH EARLY FRIDAY...LARGEST
ACCUMULATIONS ARE TO CLUSTER BETWEEN SOUTHERN VERACRUZ TO SOUTHERN
BELIZE/NORTHERN GUATEMALA...WHERE EXPECTING 10-15MM/DAY AND MAXIMA
OF 20-40MM. BY FRIDAY-SATURDAY...AS A MOIST PLUME ARRIVES FROM THE
EAST...EXPECTING AN INCREASE IN ACCUMULATIONS IN SOUTHERN
BELIZE/EASTERN GUATEMALA AND NORTHERN HONDURAS/NORTHEASTERN
NICARAGUA TO 15-20MM/DAY AND MAXIMA OF 30-60MM. BY
SATURDAY-SUNDAY...UNDER THE INFLUENCE OF THE TROPICAL
WAVE...EXPECTING SIMILAR AMOUNTS EXPANDING INTO ALL OF BELIZE AND
EASTERN GUATEMALA. ALSO UNDER THE INFLUENCE OF THE TROPICAL
WAVE...EXPECTING SOME CONVECTION TO DEVELOP IN THE PACIFIC BASIN
TO PRODUCE 10-15MM/DAY AND MAXIMA OF 20-40MM BETWEEN THE GULF OF
FONSECA/NORTHWESTERN NICARAGUA AND SOUTHERN GUATEMALA.

IN SOUTHERN CENTRAL AMERICA...ACTIVE CONVECTION IS TO PERSIST
THROUGH THE CYCLE UNDER THE INFLUENCE OF A MOISTURE POOL THAT
EXCEEDS 60MM...AND A MODERATELY ORGANIZED PANAMANIAN LOW.
FURTHERMORE...ADDITIONAL ENHANCEMENT IS EXPECTED WITH THE
APPROACHING TROPICAL WAVE. IN COSTA RICA...EXPECTING 10-15MM/DAY
AND MAXIMA OF 20-40MM IN A DAILY BASIS...WHEREAS IN
PANAMA...EXPECTING A PEAK ON FRIDAY-SATURDAY WHERE AMOUNTS ARE TO
INCREASE FROM 05-10MM/DAY AND MAXIMA OF 15-20MM TO 10-15MM/DAY AND
MAXIMA OF 20-45MM.

IN THE CARIBBEAN...A TRADE WIND SURGE CONTINUES PROPAGATING
WESTWARD WHILE LEADING TO WINDY AND DRY CONDITIONS BEHIND THE
LEADING EDGE. THIS SURGE IS ASSOCIATED WITH WINDS OF 20-35KT...A
SUBSIDENCE CAP THAT SITS NEAR 900 HPA...AND VERY DRY MID-LEVELS.
BY LATE THURSDAY...THE SURGE EDGE WILL EXTEND ACROSS THE EASTERN
DOMINICAN REPUBLIC...BY FRIDAY EVENING IT WILL EXTEND ACROSS
WESTERN HAITI...AND BY SATURDAY EVENING IT WILL EXTEND WEST OF
JAMAICA AND CLOSE TO THE CAYMAN ISLANDS. AHEAD OF THE
SURGE...ENHANCED MOISTURE CONVERGENCE WILL CONTINUE SUSTAINING
ACTIVE CONVECTION. THIS IS REINFORCED BY THE INFLUENCE OF A
TROPICAL WAVE. BY EARLY FRIDAY...LARGEST RAINFALL ACCUMULATIONS
ARE EXPECTED IN THE DOMINICAN REPUBLIC AND EASTERN JAMAICA WHERE
EXPECTING 10-15MM/DAY AND MAXIMA OF 20-35MM. SIMILAR AMOUNTS ARE
EXPECTED IN JAMAICA ON FRIDAY-EARLY SATURDAY...AND A SHARP
DECREASE IS EXPECTED AFTER.

ALSO IN THE CARIBBEAN...AS THE TRADE WIND SURGE PROPAGATES ACROSS
THE NORTHERN TIER...THE ITCZ IS TO CONFINE TO THE WINDWARD
ISLANDS/SOUTHERN CARIBBEAN...ENTERING THE BASIN THROUGH TRINIDAD
AND TOBAGO. NOTE THAT TRADE WINDS WILL ALSO REMAIN FAST...BETWEEN
15-30KT...YET UNDER THE INFLUENCE OF THE MOIST PLUME...EXPECTED
MODERATE RAINFALL AMOUNTS. LARGEST ACCUMULATIONS ARE EXPECTED IN
THE SOUTHERN WINDWARD ISLANDS/NORTHEASTERN VENEZUELA...WHERE
AMOUNTS ARE TO GRADUALLY DECREASE FROM 15-20MM/DAY AND MAXIMA OF
25-50MM ON THURSDAY...TO 10-15MM/DAY AND MAXIMA OF 20-40MM BY
SATURDAY. IN THE ABC ISLANDS AND NORTHERN VENEZUELA...EXPECTING A
GRADUAL INCREASE FROM 05-10MM/DAY AND MAXIMA OF 15-25MM ON
THURSDAY...TO 10-15MM/DAY AND MAXIMA OF 20-35MM ON SATURDAY.

IN NORTHERN SOUTH AMERICA...LARGEST ACCUMULATIONS WILL CLUSTER IN
COLOMBIA...WHERE ENHANCED CONVECTIVE INSTABILITY AND WESTERLIES
ACROSS THE PACIFIC BASIN WILL CONTINUE TO SUSTAIN THE CURRENT
SEASONALLY ACTIVE PATTERN OF CONVECTION. EXPECTING AMOUNTS OF
15-20MM/DAY AND MAXIMA OF 25-50MM THROUGH EARLY
SATURDAY...INCREASING TO 15-20MM/DAY AND MAXIMA OF 35-70MM BY
SATURDAY-SUNDAY.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL   24    36    48    60    72    84    96   TYPE  SOF
36W      40W   43W   46W   49W   52W   55W   58W   TW    20N
72W      74W   77W   80W   82W   84W   87W   89W   TW    18N
90W      92W   94W   96W   DISSIPATES              TW    24N

A TROPICAL WAVE IS INITIALIZED AT 36W. THIS WAVE APPROACHES THE
BASIN ON SUNDAY TO START ENHANCING ACTIVITY IN THE GUIANAS.

TROPICAL WAVE INITIALIZED AT 72W WILL CONTINUE STIMULATING
CONVECTION AS IT PROPAGATES WEST ACROSS THE CARIBBEAN BASIN. ON
THURSDAY/FRIDAY...THE WAVE WILL ENHANCE ACCUMULATIONS IN JAMAICA
TO PRODUCE 10-15MM/DAY AND MAXIMA OF 20-35MM. ALSO DURING THIS
PERIOD...THIS WILL SUSTAIN AMOUNTS OF 15-20MM/DAY AND MAXIMA OF
25-50MM IN COLOMBIA. IN PANAMA AND COSTA RICA...THE WAVE WILL
ENHANCE ACTIVITY TO SUSTAIN AMOUNTS OF 10-15MM/DAY AND MAXIMA OF
20-45MM ON FRIDAY-SATURDAY. BY SATURDAY-SUNDAY...ENHANCEMENT WILL
CONCENTRATE IN CENTRAL AMERICA. LARGEST ACCUMULATIONS ARE EXPECTED
IN THE GULF OF HONDURAS...WHERE THE WAVE IN INTERACTION WITH A
LOW-LEVEL JET WILL FAVOR AMOUNTS OF 15-20MM/DAY AND MAXIMA OF
30-60MM. NOTE THAT THERE IS A CHANGE FOR ISOLATED HIGHER AMOUNTS
IN REGION OF OROGRAPHIC FORCING.

A TROPICAL WAVE INITIALIZED AT 90W CONTINUES TO BE ILL-DEFINED AND
HAS LIMITED EFFECT ON THE PRECIPITATION IN CONTINENTAL REGIONS.

GUY...NMS (BELIZE)
PECK...MS (JAMAICA)
GALVEZ...WPC (USA)
$$





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