Prognostic Meteorological Discussion
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM EDT THU MAR 23 2017

TROPICAL DISCUSSION FROM MARCH 23/12 UTC: CONSISTENT WITH PREVIOUS
FORECASTS...A MID/UPPER LEVEL TROUGH IS TO PULL ACROSS THE
SOUTHWEST USA...MOVING ACROSS OKLAHOMA/TEXAS ON FRIDAY
EVENING...AND TO THE MISSISSIPPI BASIN ON SATURDAY. THE TROUGH IS
TO PRESS AGAINST A RIDGE TO THE EAST AND SOUTH. UNDER PRESSURE THE
RIDGE OVER MEXICO IS TO GRADUALLY WEAKEN/NEARLY COLLAPSE ON
FRIDAY. AS THE RIDGE WEAKENS IT IS TO FAVOR GRADUAL EROSION OF MID
LEVEL CAP INVERSION OVER MEXICO...WITH DEEPER INSTABILITY ON THE
SOUTHWEST STATES OF MEXICO ON FRIDAY TO SATURDAY TO FAVOR AN
INCREASE IN DIURNAL CONVECTION. EARLY IN THE CYCLE EXPECTING
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM. THROUGH
SATURDAY THIS WILL INCREASE TO 10-15MM/DAY AND MAXIMA OF 20-30MM.
AT LOW LEVELS...THE ASSOCIATED FRONT IS TO CONFINE TO THE
SOUTHWEST USA/EXTREME NORTHERN PORTIONS OF MEXICO EARLY IN THE
CYCLE...WITH CONVECTION LIMITING TO NORTH OF THE BORDER.

A MID LEVEL RIDGE OVER THE EASTERN USA FAVORS THE SOUTHWARD
AMPLIFICATION OF A LONG WAVE TROUGH ACROSS THE WESTERN ATLANTIC TO
THE NORTHWEST CARIBBEAN...WHERE IT IS TO PHASE WITH A SHORT WAVE
TROUGH TO THE SOUTH. AS THE MID LEVEL RIDGE ENCROACHES INTO THE
WESTERN ATLANTIC ON FRIDAY-SATURDAY...IT IS TO UNDERCUT THE TROUGH
TO THE EAST. THIS IS TO THEN EVOLVE INTO A MID LEVEL LOW OVER THE
BAHAMAS WHILE A SHORT WAVE TROUGH REMAINS OVER THE
CENTRAL/SOUTHERN CARIBBEAN TO SOUTHERN CENTRAL AMERICA. EARLY IN
THE CYCLE THE AMPLIFYING TROUGH WILL PRESS AGAINST A CELL OF THE
SUBEQUATORIAL RIDGE TO THE SOUTH AND EAST. THIS IS TO TIGHTEN THE
GRADIENT WHILE FAVORING INTENSIFICATION OF A SUBTROPICAL JET
MAXIMA ROUNDING THE BASE OF THE LONG WAVE TROUGH. THE JET MAXIMA
IS TO SLOWLY LIFT ACROSS THE CENTRAL CARIBBEAN-HISPANIOLA.
DIVERGENCE ON ITS RIGHT ENTRANCE REGION IS TO VENT DEEP CONVECTION
ACROSS SOUTHERN CENTRAL AMERICA-COLOMBIA/NORTHWEST VENEZUELA EARLY
IN THE CYCLE...AND ACROSS HISPANIOLA-PUERTO RICO/VIRGIN ISLES ON
FRIDAY THROUGH SUNDAY. AS THE SUBEQUATORIAL RIDGE YIELDS TO THE
POLAR TROUGH...TRADE WINDS CAP OVER THE NORTHEAST CARIBBEAN IS TO
GRADUALLY WEAKEN THROUGH FRIDAY. THIS...IN-TURN...WILL FAVOR
DEEPER LAYER CONVECTIVE INSTABILITY OVER THE NORTHEAST CARIBBEAN
ISLES DURING THE NEXT FEW DAYS.

AT LOW LEVELS...BROAD RIDGE OVER THE EASTERN USA IS DRIVING A
POLAR FRONT SOUTH ACROSS THE WESTERN ATLANTIC TO THE NORTHWEST
BAHAMAS. THROUGH FRIDAY MORNING THE FRONT WILL MEANDER SOUTH TO
THE CENTRAL BAHAMAS...AND LATER IN THE DAY IT IS TO BOTTOM OUT
ALONG 22N/23N WHILE MEANDERING OVER THE BAHAMAS TO THE FLORIDA
PENINSULA. AS IT ENTERS THE NORTHWEST BAHAMAS THE FRONT WILL
SUSTAIN RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM
THROUGH FRIDAY MORNING...WHILE OVER THE CENTRAL/SOUTHEAST BAHAMAS
AND THE TURKS IT IS TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15MM ON FRIDAY-SATURDAY. ALSO...THE SURGING FRONT IS TO
SUSTAIN A PREFRONTAL SHEAR LINE ACROSS HISPANIOLA-CENTRAL
CARIBBEAN EARLY IN THE CYCLE...WHERE IT IS TO MEANDER DURING THE
NEXT 48-54 HRS. THE SHEAR LINE WILL FAVOR STRONG BOUNDARY LAYER
WINDS OF 20-25KT ACROSS HISPANIOLA-JAMAICA. THE STRONG WINDS WILL
FAVOR TOPOGRAPHICALLY INDUCED CONVECTION ACROSS
HISPANIOLA...TRIGGERING RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA
OF 30-60MM THROUGH FRIDAY MORNING. ON FRIDAY TO SATURDAY...UNDER
FAVORABLE JET DYNAMICS...THIS WILL INCREASE TO 30-60MM/DAY AND
MAXIMA OF 75-125MM. OVER JAMAICA...INITIALLY EXPECTING RAINFALL
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM. ON FRIDAY...AS THE
WINDS SURGE ACROSS THE WINDWARD CHANNEL/HAITIAN PENINSULA...AND
WITH DEW POINT TEMPERATURES OF 18-19C...THIS WILL INCREASE TO
15-20MM/DAY AND MAXIMA OF 25-50MM...WITH MOST INTENSE ON THE
NORTHEAST PARISHES.

THE DEEP POLAR TROUGH OVER THE WESTERN ATLANTIC ALSO FAVORS AN
INDUCED/PREFRONTAL TROUGH ACROSS THE CENTRAL CARIBBEAN/HISPANIOLA.
THIS...IN COMBINATION WITH BROAD RIDGE OVER THE CENTRAL/EASTERN
ATLANTIC FAVORS A MOIST SOUTHEASTERLY FLOW ACROSS THE ISLAND CHAIN
TO PUERTO RICO/VIRGIN ISLES. THROUGH FRIDAY THIS IS TO FAVOR AN
INCREASE IN MOISTURE CONTENT...WITH PWAT EXPECTED TO PEAK AROUND
50MM. THIS WILL COMBINE WITH UPPER TROUGH PATTERN/FAVORABLE JET
DYNAMICS TO SUSTAIN AN INCREASE IN CONVECTION. EARLY IN THE CYCLE
EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-45MM.
ON FRIDAY THIS INCREASES TO 20-30MM/DAY AND MAXIMA OF
50-100MM...WHILE ON SATURDAY IT DECREASES TO 15-20MM/DAY AND
MAXIMA OF 35-70MM. OTHER CONVECTION IS EXPECTED OVER THE
LEEWARD/VIRGIN ISLES...WITH RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-25MM ON FRIDAY...AND 00-05MM/DAY AND MAXIMA OF 10MM
ON SATURDAY. LATER DURING THE WEEKEND...UNDER THE INFLUENCE OF THE
MID LEVEL CYCLONE OVER THE BAHAMAS...THE INDUCED TROUGH IS TO
EVOLVE INTO A CLOSED LOW JUST NORTH OF HISPANIOLA/EAST OF THE
TURKS AND CAICOS. NOTE THAT SOME OF THE MODELS SUGGEST POSSIBILITY
OF SUBTROPICAL CYCLONE FORMING AS THE LOW LEVEL CIRCULATION
EVOLVES INTO A WARM CORE SYSTEM. THE LOW WILL BECOME FOCUS OF LOW
LEVEL MOISTURE CONVERGENCE...WITH ORGANIZED DEEP CONVECTION TO
CLUSTER ALONG THIS FEATURE. ACROSS HISPANIOLA AND THE TURKS THIS
IS TO THEN FAVOR RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF
25-50MM. OVER THE SOUTHERN CARIBBEAN...UNDER FAVORABLE JET
DYNAMICS EARLY IN THE CYCLE....EXPECTING CONVECTION ON THE
CARIBBEAN COASTAL PLAINS OF COSTA RICA-BOCAS DEL TORO IN WESTERN
PANAMA TO INCREASE TO 15-20MM/DAY AND MAXIMA OF 25-50MM DURING THE
DAY TODAY. ON FRIDAY-SATURDAY THIS DECREASES TO 10-15MM/DAY AND
MAXIMA OF 20-35MM. THIS IS TO ALSO INDUCE A SURGE IN CONVECTION
ACROSS NORTHERN COLOMBIA AND VENEZUELA...WITH MOST ACTIVE OVER
COLOMBIA TO CLUSTER BETWEEN THE EJE CAFETERO AND THE SIERRA NEVADA
DE SANTA MARTA...WHILE OVER VENEZUELA EXPECTING MOST INTENSE TO
THE NORTHWEST...WITH RAINFALL AMOUNTS OF 30-40MM/DAY AND MAXIMA OF
75-125MM. AS THE JET PULLS ON FRIDAY THIS DECREASES TO 15-30MM/DAY
AND MAXIMA OF 40-80MM...WHILE ON SATURDAY EXPECTING RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM. THIS IS TO ALSO
ENHANCE CONVECTION ACROSS THE ABC ISLES/NORTH COAST OF
VENEZUELA...TO RESULT IN RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-20MM. THROUGH SATURDAY MAXIMA DECREASES TO 15MM/DAY
IN SCATTERED CONVECTION.

THE SUBEQUATORIAL RIDGE TO THE SOUTH EXTENDS WEST ACROSS THE
TROPICAL ATLANTIC TO NORTHERN SOUTH AMERICA. THE RIDGE IS TO HOLD
DURING THE NEXT FEW DAYS. ACROSS THE GUIANAS DIURNAL
CONVECTION/SEA BREEZE CONVERGENCE IS TO FAVOR RAINFALL AMOUNTS OF
00-05/DAY AND WIDELY ISOLATED MAXIMA OF 10MM/DAY THROUGH SUNDAY
MORNING. HIGHER AMOUNTS ARE EXPECTED OVER AMAZONIA IN SOUTHERN
VENEZUELA AND COLOMBIA...WHERE DIURNAL/NEAR EQUATORIAL TROUGH
RELATED CONVECTION IS TO SUSTAIN RAINFALL AMOUNTS OF 15-20MM/DAY
AND MAXIMA OF 25-50MM IN SCATTERED CONVECTION.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL   24     36     48     60     72     84     96       TYPE
17W      20W    23W    26W    30W    32W    36W    40W       TW
27W      31W    35W    38W    40W    42W    44W    47W       TW

TROPICAL WAVE ALONG 17W AND 27W WILL CONFINE TO THE ATLANTIC ITCZ
DURING THE NEXT FEW DAYS.

JIMENEZ...IMN (COSTA RICA)
SUBRATH-ALI...TTMS (TRINIDAD AND TOBAGO)
DAVISON/GALVEZ...WPC (USA)

$$





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