Prognostic Meteorological Discussion
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FXCA20 KWBC 281838
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 PM EDT FRI APR 28 2017

TROPICAL DISCUSSION FROM APRIL 28/12 UTC: DEEPENING POLAR TROUGH
MOVES ACROSS THE SOUTHWEST USA EARLY IN THE CYCLE. THE AMPLIFYING
TROUGH IS PRESSING AGAINST A MID LEVEL RIDGE TO THE SOUTH...AS THE
LATTER EXTENDS OVER THE SOUTHERN STATES OF MEXICO-CENTRAL AMERICA
TO THE WESTERN CARIBBEAN. THE RIDGE IS TO GENERALLY HOLD OVER THE
NEXT FEW DAYS...WHILE THE TROUGH BOTTOMS OUT OVER THE NORTHERN
STATES OF MEXICO LATER ON SATURDAY. AT LOW LEVELS THE TROUGH WILL
SUSTAIN A FRONT THAT MOVES ACROSS TEXAS TO NORTHEAST MEXICO LATER
ON SATURDAY. THROUGH SUNDAY AFTERNOON IT MOVE ACROSS TAMAULIPAS TO
NORTHERN VERACRUZ...WHERE IT IS TO STALL. THIS IS TO THEN SUSTAIN
A PREFRONTAL TROUGH ON THE SOUTHERN STATES OF MEXICO/CAMPECHE
SOUND. THIS IS TO ENHANCE LOW LEVEL MOISTURE CONVERGENCE ON SUNDAY
TO FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-30MM.

THE MID LEVEL RIDGE...AS IT HOLDS TO THE SOUTH...IS TO SUSTAIN A
MID LEVEL CAP INVERSION. THIS WILL BE STRONG ENOUGH TO DELAY ONSET
OF DIURNAL CONVECTION...BUT NOT STRONG ENOUGH TO SUPPRESS IT.
ACTIVITY IS TO GENERALLY CLUSTER ALONG THE CONTINENTAL DIVIDE
BETWEEN CHIAPAS IN SOUTHERN MEXICO-SOUTHERN GUATEMALA TO SOUTHERN
HONDURAS/EL SALVADOR. IN THIS AREA EXPECTING RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15-20MM. OVER SOUTHERN CENTRAL
AMERICA...DEEP LAYER CONVECTIVE INSTABILITY PERSISTS...ALLOWING
FOR DEEPER MOISTURE TO POOL OVER SOUTHERN NICARAGUA-COSTA
RICA-PANAMA. ON THE CARIBBEAN COASTAL PLAINS OF SOUTHERN
NICARAGUA-BOCAS DEL TORO IN PANAMA TRADE WIND CONVERGENCE WILL
FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM. HIGHER
AMOUNTS ARE TO CLUSTER ON THE PACIFIC SIDE OF THE ISTHMUS...AS
ENHANCED BY A LOW LEVEL SOUTHWESTERLY FLOW. THIS IS TO FAVOR LATE
AFTERNOON CONVECTION...WITH MOST ACTIVE EXPECTED ALONG THE
CONTINENTAL DIVIDE. IN THIS AREA EXPECTING RAINFALL ACCUMULATION
OF 15-20MM/DAY AND MAXIMA OF 30-60MM. THIS IS FORECAST TO
GRADUALLY INTENSIFY THROUGH SATURDAY EVENING...WHEN WE EXPECT
RAINFALL AMOUNTS OF 15-30MM/DAY AND MAXIMA OF 40-80MM...WHILE ON
SUNDAY IT DECREASES TO 10-15MM/DAY AND MAXIMA OF 20-40MM.

AS THE EASTERN PACIFIC ITCZ MEANDERS SOUTH OF PANAMA INTO
NORTHWEST COLOMBIA...THIS IS TO FAVOR SCATTERED DEEP
CONVECTION...WITH ACCUMULATION OF 15-20MM/DAY AND MAXIMA OF
30-60MM. ON SATURDAY THIS INCREASES TO 15-20MM/DAY AND MAXIMA OF
35-70MM. ON THE SIERRA NEVADA TO THE NORTH AND NORTHWEST VENEZUELA
EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM.
THIS INCREASES ON SATURDAY/SUNDAY TO 10-15MM/DAY AND MAXIMA OF
20-35MM. OVER SOUTHWEST COLOMBIA EXPECTING RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15-20MM. THROUGH SUNDAY THIS INCREASES
TO 10-15MM/DAY AND MAXIMA OF 20-30MM AS ENHANCED BY A LOW/MID
LEVEL WESTERLY FLOW. ON THE PIEDEMONTE LLANERO IN SOUTHWESTERN
COLOMBIA A SOUTHERN HEMISPHERE WIND SURGE IS TO FAVOR RAINFALL
AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 30-60MM...GRADUALLY
DECREASING TO 10-15MM/DAY AND MAXIMA OF 20-40MM ON SUNDAY-MONDAY.
HIGHER AMOUNTS ARE EXPECTED ACROSS AMAZONIA TO THE EAST INTO
SOUTHERN VENEZUELA. IN THIS AREA A SOUTHERN HEMISPHERE PREFRONTAL
SHEAR LINE IS TO SUSTAIN RAINFALL AMOUNTS OF 25-50MM/DAY AND
MAXIMA OF 75-125MM THROUGH SATURDAY MORNING....15-20MM/DAY AND
MAXIMA OF 35-70MM ON SATURDAY TO SUNDAY...WHILE ON SUNDAY TO
MONDAY EXPECTING ACCUMULATION OF 10-15MM/DAY AND MAXIMA OF 20-40MM
AS THE SHEAR LINE WEAKENS.

DEEPENING POLAR TROUGH OVER THE WESTERN USA IS TO THEN INDUCE THE
GRADUAL INTENSIFICATION OF A MID/UPPER LEVEL RIDGE TO THE EAST.
THE RIDGE IS TO ANCHOR ON A 500 HPA HIGH OFF THE MID ATLANTIC
REGION IN THE USA. A TUTT TO THE SOUTH OF THIS RIDGE LIES TO THE
NORTH-NORTHEAST OF THE BAHAMAS. THE RIDGE...AS IT MEANDERS OVER
THE WESTERN ATLANTIC...WILL GRADUALLY DISPLACE THE TROUGH TO THE
EAST-SOUTHEAST...NEARING THE NORTHEAST CARIBBEAN ISLES LATER THIS
EVENING/EARLY SATURDAY MORNING. THIS IS TO THEN REMAIN NEARLY
STATIONARY. A JET MAXIMA ACCOMPANIES THE UPPER LEVEL FEATURE...AND
AS IT ROUNDS THE BASE OF THE TROUGH IT IS TO FAVOR AN UPPER
DIVERGENT PATTERN OVER THE DOMINICAN REPUBLIC LATER TODAY...AND
PUERTO RICO ON SATURDAY. THE JET MAXIMA IS TO THEN PULL AWAY AS
ANOTHER APPROACHES FROM THE WEST. THE JET MAXIMA THEN PLUNGES
ACROSS HISPANIOLA EARLY ON SUNDAY MORNING...WITH ITS LEFT EXIT
REGION REPOSITIONING TO THE SOUTH-SOUTHWEST OF PUERTO RICO DURING
THE DAY...THIS WILL LIKELY RESULT IN AN INDIRECT AGEOSTROPHIC
CIRCULATION ACROSS THE NORTHEAST CARIBBEAN ISLES ON SUNDAY. AT MID
LEVELS...A CLOSED LOW IS TO MEANDER JUST NORTH OF THE DOMINICAN
REPUBLIC EARLY ON SATURDAY EVENING...TO JUST NORTH OF PUERTO
RICO/VIRGIN ISLES ON SUNDAY-MONDAY. THE MEANDERING TROUGH IS TO
FAVOR CYCLONIC VORTICITY ADVECTION...MOST INTENSE OVER PUERTO
RICO-VIRGIN ISLES IS EXPECTED DURING THE WEEKEND. THIS WILL
COMBINE WITH FAVORABLE UPPER LEVEL JET DYNAMICS TO SUSTAIN
ORGANIZED DEEP CONVECTION. AT LOW LEVELS...BROAD RIDGE OVER THE
WESTERN ATLANTIC/NORTH OF THE ISLANDS SUSTAINS A TIGHT GRADIENT
ACROSS THE BASIN. OVER THE EASTERN/NORTHERN CARIBBEAN ISLES THIS
FAVOR BOUNDARY LAYER WINDS OF 15-20KT...WHILE OVER THE SOUTHERN
CARIBBEAN/COAST OF COLOMBIA THE WINDS PEAK AT 20-30KT. THIS IS
ENHANCING MOISTURE CONVERGENCE ACROSS THE LEEWARD ISLES AND THE
NORTHEAST CARIBBEAN...A PATTERN THAT THE MODELS FORESEE TO LAST
THROUGHOUT THE WEEKEND/EARLY NEXT WEEK. UNDER INFLUENCE OF THE
UPPER TROUGH...AN INDUCED TROUGH IN THE EASTERLY TRADES FORMS OVER
THE EASTERN CARIBBEAN EARLY NEXT WEEK. IN RESPONSE...THE LOW LEVEL
WINDS ARE NOW EXPECTED TO GRADUALLY VEER TO THE SOUTHEAST. THIS
WILL HELP SUSTAIN HIGH PRECIPITABLE WATER CONTENT...PEAKING AROUND
50MM OVER PUERTO RICO ON SATURDAY...AND THE VIRGIN-LEEWARD ISLES
ON SUNDAY-MONDAY. OVER EASTERN CUBA-JAMAICA AND HAITI EXPECTING
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM. ACROSS THE
DOMINICAN REPUBLIC AND PUERTO RICO EXPECTING RAINFALL AMOUNTS OF
15-30MM/DAY AND MAXIMA OF 40-80MM THROUGH SATURDAY MORNING. ON
SATURDAY TO SUNDAY IT WILL INCREASE TO 20-30MM/DAY AND MAXIMA OF
50-100MM. ON SUNDAY FOCUS OF THE HEAVY CONVECTION SHIFTS EAST
ACROSS PUERTO RICO-VIRGIN ISLES...WHERE CONDITIONS BECOME
FAVORABLE FOR AN MCS TO FORM...WITH ACCUMULATION OF 25-50MM/DAY
AND MAXIMA OF 75-125MM IN POTENTIALLY SEVERE CONVECTION AS
ENHANCED BY UPPER LEVEL JET MAXIMUM. OVER THE EASTERN CARIBBEAN
ISLES CONVECTION IS TO INITIALLY CLUSTER OVER THE SOUTHERN
LEEWARD/FRENCH ISLES...WHERE WE EXPECT RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-30MM. AS THE TUTT DEEPENS TO THE
NORTH THIS WILL DRAW THE MOISTURE NORTH...SPREADING TO THE
NORTHERN LEEWARD-VIRGIN ISLES...TO SUSTAIN RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-35MM.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL   24     36     48     60     72     84     96       TYPE
31W      34W    38W    41W    45W    49W    52W    56W       TW
50W      54W    57W    60W    63W    67W    71W    74W       TW
60W      63W    66W    69W    72W    DISSIPATES              TW
72W      73W    75W    77W    79W    80W    DISSIPATES       TW

A TROPICAL WAVE IS INITIALIZED ALONG 31W AND SOUTH OF 06N. THE
WAVE REACHES FRENCH GUIANA ON MONDAY TO TRIGGER RAINFALL AMOUNTS
OF 10-15MM/DAY AND MAXIMA OF 20-35MM.

A TROPICAL WAVE IS INITIALIZED ALONG 50W AND SOUTH OF 06N. THIS
SUSTAINS A MOIST SURGE THAT IS TO QUICKLY SPREAD ACROSS FRENCH
GUIANA TO SURINAME-GUYANA...INTO THE SOUTHERN WINDWARD
ISLES/SOUTHEAST CARIBBEAN-NORTHERN VENEZUELA DURING THE WEEKEND.
OVER THE GUIANAS IT IS TO SUSTAIN RAINFALL AMOUNTS OF 10-15MM/DAY
AND MAXIMA OF 20-45MM THROUGH SATURDAY...DECREASING TO 10-15MM/DAY
AND MAXIMA OF 20-30MM ON SATURDAY TO SUNDAY. LATER ON SATURDAY
CONVECTION IS TO SPREAD ACROSS NORTHERN GUYANA TO NORTHEAST
VENEZUELA TO THE SOUTHERN WINDWARD ISLES/TRINIDAD AND
TOBAGO...WHERE IT IS TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-25MM. OVER CENTRAL-SOUTHERN VENEZUELA IT IS TO THEN
TRIGGER RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM ON
SUNDAY.

A TROPICAL WAVE IS INITIALIZED ALONG 60W AND SOUTH OF 06N. ACROSS
SOUTHERN VENEZUELA IT IS TO INTERACT WITH A PREFRONTAL SHEAR LINE
AND THE NEAR EQUATORIAL TROUGH TO SUSTAIN ORGANIZED DEEP
CONVECTION...WITH ACCUMULATION OF 25-50MM/DAY AND MAXIMA OF
75-125MM. OVER COLOMBIA IT IS TO THEN TRIGGER RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-40MM. THROUGH SUNDAY IT IS NOW
EXPECTED TO DISSIPATE.

A TROPICAL WAVE IS INITIALIZED ALONG 72W AND SOUTH OF 06N. THIS
TENDS TO WEAKEN AS IT CROSSES THE ANDES LATER DURING THE WEEKEND.
MEANWHILE...ACROSS SOUTHERN COLOMBIA IT IS TO SUSTAIN RAINFALL
AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 30-60MM.

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





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