Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2
000
FXCA20 KWBC 241811
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
211 PM EDT MON APR 24 2017

TROPICAL DISCUSSION FROM APRIL 24/12 UTC: AT 500 HPA...A POLAR
TROUGH OVER THE SOUTHEAST USA/GULF OF MEXICO SUSTAINS THE
NORTHWARD AMPLIFICATION OF A RIDGE OVER THE WESTERN ATLANTIC/NORTH
OF THE GREATER ANTILLES. LATER THIS AFTERNOON THE TROUGH WILL
EXTEND FROM THE SOUTHEAST USA TO THE EASTERN GULF/CUBA-NORTHWEST
CARIBBEAN. A SUBTROPICAL JET ROUNDING THE BASE OF THE TROUGH IS TO
EXIT JUST SOUTH OF HISPANIOLA LATER THIS AFTERNOON. ON
TUESDAY...AS THE TROUGH LIFTS TO THE NORTH-NORTHEAST...THE JET
WILL RELOCATE TO JUST SOUTH OF PUERTO RICO. ON ITS LEFT EXIT
REGION AN UPPER DIVERGENT PATTERN IS TO ENVELOP MOST OF HISPANIOLA
DURING THE DAY TODAY...AND PUERTO RICO BY MIDDAY/AFTERNOON ON
TUESDAY. OVER HISPANIOLA TO THE NORTHERN LEEWARD ISLES THIS IS TO
ALSO FAVOR DEEP LAYER CONVECTIVE INSTABILITY...WITH PWAT CONTENT
OF 40-50MM EARLY IN THE CYCLE. THROUGH WEDNESDAY MORNING THE
MODELS AGREE ON GRADUAL EROSION OF AVAILABLE MOISTURE AS MID LEVEL
CAP STRENGTHENS OVER THE NORTHERN CARIBBEAN ISLES. AT LOW LEVELS
THE TROUGH ALOFT SUSTAINS A SURFACE FRONT THAT IS TO EXTEND FROM A
LOW OVER THE SOUTHEAST USA...ACROSS THE FLORIDA KEYS TO-WESTERN
CUBA-NORTHERN YUCATAN LATER TODAY. THROUGH TUESDAY MORNING THE
FRONT WILL MOVE TO THE NORTHWEST BAHAMAS WHILE TRAILING ACROSS
WESTERN CUBA TO THE NORTHERN YUCATAN. BOUNDARY IS TO THEN REMAIN
NEARLY STATIONARY THROUGH WEDNESDAY MORNING...WITH ITS TRAILING
END LIFTING OVER THE GULF AS THE FRONT DISSIPATES ON WEDNESDAY TO
THURSDAY. ALSO AT LOW LEVELS...A RIDGE LIES TO THE EAST OF THE
POLAR TROUGH...FAVORING A MOIST SOUTHEASTERLY FLOW ACROSS THE
LESSER ANTILLES TO PUERTO RICO-HISPANIOLA. THIS WILL HELP SUSTAIN
A HIGH MOISTURE CONTENT DURING THE NEXT TWO DAYS. DURING THE DAY
ON WEDNESDAY...AS THE FRONT/POLAR TROUGH WEAKENS...THE RIDGE WILL
BUILD TO THE WEST. THE LOW LEVEL WINDS WILL THEN BACK TO THE EAST
ACROSS THE ENTIRE BASIN.

MEANWHILE...OVER THE CENTRAL/NORTHWEST BAHAMAS THE MEANDERING
FRONT WILL TRIGGER  LIGHT RAINFALL AMOUNTS. OVER CENTRAL-EASTERN
CUBA EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM.
OVER THE YUCATAN/SOUTHERN MEXICO THIS IS TO ONLY FAVOR LIGHT
RAINFALL AMOUNTS IN ISOLATED CONVECTION. STRONG MESO-SYNOPTIC
FORCING OVER HISPANIOLA IS TO FAVOR RAINFALL AMOUNTS OF
25-50MM/DAY AND MAXIMA OF 75-125MM THROUGH TUESDAY MORNING...AND
05-10MM/DAY AND MAXIMA OF 15-20MM ON TUESDAY TO WEDNESDAY. ACROSS
PUERTO RICO INITIALLY EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY
AND MAXIMA OF 20-40MM THROUGH TUESDAY MORNING. ON TUESDAY...AS THE
UPPER TROUGH APPROACHES THE ISLAND DURING MAX HEATING...CONDITIONS
WILL BECOME FAVORABLE FOR MCS TO FORM...TRIGGERING RAINFALL
AMOUNTS OF 20-35MM/DAY AND MAXIMA OF 50-100MM. OVER THE VIRGIN
ISLES-NORTHERN LEEWARD ISLES IT IS TO THEN TRIGGER RAINFALL
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM THROUGH TUESDAY
MORNING. OVER THE FRENCH-NORTHERN WINDWARD ISLES...THE LOW LEVEL
RIDGE IS TO SUSTAIN A LOW LEVEL CONVERGENT FLOW THROUGH TUESDAY
EVENING...WITH RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM.
ON TUESDAY TO WEDNESDAY THE MAXIMA WILL INCREASE TO 15-25MM.
DRYING TREND FOLLOWS ON WEDNESDAY-THURSDAY AS THE PREVAILING
EASTERLIES RETURN...WITH RAINFALL AMOUNTS OF 00-05MM/DAY AND
MAXIMA OF 10MM.

A MID LEVEL RIDGE IS TO GRADUALLY BUILD TO THE EAST ACROSS THE
EASTERN TROPICAL PACIFIC/CENTRAL AMERICA TO THE CARIBBEAN. AT 500
HPA THE RIDGE IS TO INITIALLY CONFINE TO CENTRAL AMERICA/EASTERN
PACIFIC. ON TUESDAY IT IS TO EXPAND TO THE CENTRAL CARIBBEAN...AND
THROUGH WEDNESDAY EVENING IT IS TO SETTLE ACROSS THE BASIN TO
NORTHERN SOUTH AMERICA. THIS IS TO THEN STRENGTHEN THE TRADE WINDS
CAP ACROSS THE NORTHERN CARIBBEAN ISLES...SUSTAINING A DRYING
TREND. ACROSS CENTRAL AMERICA...DIURNAL CONVECTION IS TO INITIALLY
CLUSTER ACROSS SOUTHERN HONDURAS-NORTHERN EL SALVADOR...WITH
ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-25MM. ON TUESDAY IT
INCREASES TO 10-15MM/DAY AND MAXIMA OF 20-30MM...WHILE ON
WEDNESDAY EXPECTING ACCUMULATION OF 00-05MM/DAY AND MAXIMA OF
10MM. OVER PANAMA-COSTA RICA...MEANWHILE...EXPECTING RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM.

POLAR TROUGH ENTERING THE WESTERN USA ON TUESDAY IS TO THEN PRESS
AGAINST THE BUILDING MID LEVEL RIDGE TO THE SOUTH. THE RIDGE IS TO
HOLD ITS GROUND...AND AS A RESULT THE POLAR TROUGH IS TO RAPIDLY
PULL AS IT MOVES TO THE MISSISSIPPI VALLEY LATER IN THE DAY/EARLY
THURSDAY MORNING. AT LOW LEVELS THE ASSOCIATED FRONT BOTTOMS OUT
OVER SOUTH TEXAS-RIO BRAVO LATER ON WEDNESDAY. LACKING UPPER LEVEL
SUPPORT THIS IS TO HAVE LITTLE TO NO IMPACT ACROSS THE FORECAST
AREA.

POLAR TROUGH MEANDERING OVER THE WESTERN CARIBBEAN SPLITS THE
SUBEQUATORIAL RIDGE IN TWO CELLS...WITH THE WESTERNMOST CONFINING
TO THE EASTERN PACIFIC-CENTRAL AMERICA AND THE EASTERNMOST TO THE
TROPICAL ATLANTIC/NORTHERN SOUTH AMERICA. AS THE TROUGH
PULLS...THE CELL TO THE WEST IS TO GRADUALLY BUILD ACROSS THE
BASIN TO NORTHERN SOUTH AMERICA. OVER SOUTHWEST COLOMBIA THIS IS
TO COMBINE WITH AN ONSHORE LOW LEVEL WESTERLY FLOW TO FAVOR
MODERATE TO HEAVY CONVECTION THROUGH TUESDAY MORNING...WITH
ACCUMULATION OF 15-20MM/DAY AND MAXIMA OF 35-70MM. ON TUESDAY TO
WEDNESDAY IT DECREASES TO 10-15MM/DAY AND MAXIMA OF
20-40MM...WHILE ON WEDNESDAY TO THURSDAY EXPECTING ACCUMULATION OF
05-10MM/DAY AND MAXIMA OF 15-20MM. OVER NORTHERN
COLOMBIA-NORTHWEST VENEZUELA INITIALLY EXPECTING RAINFALL AMOUNTS
OF 10-15MM/DAY AND MAXIMA OF 20-30MM. ON WEDNESDAY THIS DECREASES
TO 05-10MM/DAY AND MAXIMA OF 15-20MM. OVER AMAZONIA IN SOUTHERN
VENEZUELA-SOUTHEAST COLOMBIA EXPECT RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-45MM. THROUGH TUESDAY THIS DECREASES
TO 10-15MM/DAY AND MAXIMA OF 20-30MM. OVER THE NORTHERN GUIANAS
EXPECTING FAIR WEATHER CONDITIONS DURING THE NEXT THREE
DAYS...WITH ORGANIZED CONVECTION CONFINING TO THE NEAR EQUATORIAL
TROUGH TO THE SOUTH...WITH ACCUMULATION OF 10-15MM/DAY AND MAXIMA
OF 20-35MM/DAY.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL   24     36     48     60     72     84     96       TYPE
39W      42W    45W    48W    51W    53W    56W    59W       TW
54W      57W    59W    61W    63W    65W    67W    69W       TW

A TROPICAL WAVE IS INITIALIZED ALONG 39W AND SOUTH OF 05N. THIS
REACHES AMAPA IN BRASIL EARLY ON WEDNESDAY MORNING...TO THEN MOVE
ACROSS SOUTHERN FRENCH GUIANA LATER IN THE DAY...WHERE IT IS TO
FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM. THIS
EXPANDS ACROSS SOUTHERN SURINAME TO GUYANA ON THURSDAY...WITH
ACCUMULATION OF 10-15MM/DAY AND MAXIMA OF 20-35MM.

A TROPICAL WAVE IS INITIALIZED ALONG 54W AND SOUTH OF 08N. AS IT
MOVES ACROSS SOUTHERN SURINAME TO GUYANA THIS WILL SUSTAIN
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM THROUGH
TUESDAY MORNING...WHILE ON TUESDAY-WEDNESDAY IT IS TO AFFECT
SOUTHERN VENEZUELA WHERE IT IS TO TRIGGER RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-30MM. ACROSS SOUTHEAST COLOMBIA IT IS
TO THEN TRIGGER RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF
20-35MM...WHILE OVER THE PIEDEMONTE LLANERO EXPECTING ACCUMULATION
OF 05-10MM/DAY AND MAXIMA OF 15MM.

GAJADHAR...SLMS (SAINT LUCIA)
SUBRATH-ALI...TTMS (TRINIDAD AND TOBAGO)
DAVISON/GALVEZ...WPC (USA)
$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.