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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1814Z Apr 21, 2015)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
214 PM EDT TUE APR 21 2015

DISCUSSION FROM APRIL 21/12 UTC: A 500 HPA HIGH OVER THE CAMPECHE
SOUND ANCHORS A BROAD RIDGE THAT EXTENDS OVER THE
GULF-SOUTHERN/CENTRAL MEXICO... WESTERN CARIBBEAN-CENTRAL AMERICA.
CLOSED HIGH MEANDERS OVER THE YUCATAN EARLY IN THE CYCLE...WHILE
ASSOCIATED RIDGE BUILDS EAST ACROSS THE GREATER ANTILLES TO THE
NORTHERN LEEWARD ISLES LATER THIS EVENING. BUILDING RIDGE IS TO
STRENGTHEN THE TRADE WINDS CAP ACROSS THE NORTHERN CARIBBEAN ISLES
WHILE ALSO SUSTAINING A DRYING TREND. OVER NORTHERN CENTRAL
AMERICA TO THE SOUTHERN AND CENTRAL STATES OF MEXICO THIS IS TO
GENERALLY FAVOR A DRY AND STABLE PATTERN. HOWEVER...OVER THE
HIGHER ELEVATIONS IN SOUTHERN MEXICO-GUATEMALA TO HONDURAS/EL
SALVADOR...STRONG TOPOGRAPHICAL FORCING AND DIURNAL HEATING WILL
BE ENOUGH TO OVERCOME NEGATIVE INFLUENCE OF THE CAP INVERSION. IN
THIS AREA EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF
15-30MM IN ISOLATED TO SCATTERED CONVECTION. ON WEDNESDAY THE
DAILY MAXIMA DECREASES TO 15-20MM...WHILE ON THURSDAY-FRIDAY IT IS
EXPECTED TO PEAK AROUND 15MM. ACROSS CENTRAL CUBA EXPECTING
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM THROUGH
WEDNESDAY MORNING...DECREASING TO 00-05MM/DAY AND MAXIMA OF 10MM
ON WEDNESDAY THROUGH THURSDAY AS RIDGE STRENGTHENS ACROSS THE
NORTHERN CARIBBEAN ISLANDS.  OVER SOUTHERN CENTRAL AMERICA...MOST
ACTIVE IS EXPECTED BETWEEN PANAMA AND COSTA RICA...WITH RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-30MM.

DIGGING TROUGH ON THE SOUTHERN STREAM IS TO THEN PRESS AGAINST THE
MID LEVEL RIDGE OVER MEXICO...WITH A DEEP/HIGHLY AMPLIFIED TROUGH
TO ENTER THE NORTHWEST STATES OF MEXICO EARLY ON THURSDAY. STRONG
SUBTROPICAL JET MAXIMA IS TO DEVELOP BETWEEN THE TROUGH TO THE
NORTH AND THE RIDGE TO THE SOUTH...TO STREAM ACROSS BAJA
PENINSULA/NORTHWEST STATES OF MEXICO. THE HIGHLY AMPLIFIED TROUGH
IS TO THEN ESTABLISH A TROPICAL CONNECTION... ADVECTING DEEP
MOISTURE FROM THE ITCZ TO THE SOUTH INTO THE NORTHWEST STATES OF
MEXICO. ACROSS NORTHWEST MEXICO INFLOW OF MOISTURE AND FAVORABLE
UPPER DYNAMICS IS TO THEN SUSTAIN SCATTERED DEEP CONVECTION...TO
RESULT IN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM ON
WEDNESDAY-THURSDAY. FURTHERMORE...THIS IS TO ALSO SUSTAIN AN
INCREASE IN ACTIVITY ACROSS NORTHEAST MEXICO/RIO BRAVO LATER ON
THURSDAY...WHEN WE EXPECT RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-25MM.

DIGGING TROUGH TO THE WEST IS TO THEN INDUCE THE NORTHWARD
AMPLIFICATION OF THE MID LEVEL RIDGE ACROSS THE GULF OF MEXICO TO
THE CENTRAL USA ON WEDNESDAY TO THURSDAY. EAST AND NORTH OF THIS
AXIS...BROAD TROUGH IS TO DOMINATE THE EASTERN USA/WESTERN
ATLANTIC OVER THE NEXT FEW DAYS. AT LOW LEVELS THIS IS TO SUSTAIN
AN ELONGATED FRONT OVER THE WESTERN NORTH ATLANTIC THAT IS TO
MEANDER INTO THE FLORIDA PENINSULA JUST NORTH OF THE BAHAMAS.
ALTHOUGH FRONT STALLS TO THE NORTH OF THE BAHAMAS LATER ON
TUESDAY...A WEAK PREFRONTAL SHEAR LINE IS TO FORM OVER THE
NORTHWEST BAHAMAS BY MIDDAY ON WEDNESDAY. EARLY IN THE
CYCLE...PREFRONTAL CONVECTION OVER THE NORTHWEST BAHAMAS WILL
SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-30MM
THROUGH WEDNESDAY MORNING.

MID LEVEL TROUGH ROUNDING THE BASE OF THE LONG WAVE AXIS IS TO
QUICKLY MOVE ACROSS THE BAHAMAS THROUGH WEDNESDAY EVENING. THIS IS
TO THEN SUSTAIN A SURGE IN CONVECTION TO RESULT IN RAINFALL
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-45MM. THE SHORT WAVE
TROUGH IS TO THEN QUICKLY PULL ACROSS THE DOMINICAN REPUBLIC TO
PUERTO RICO LATER ON THURSDAY TO EARLY FRIDAY MORNING. LACKING THE
LOW LEVEL FORCING NOTED OVER THE BAHAMAS...AS IT MOVES ACROSS
HISPANIOLA TO PUERTO RICO...THE MID LEVEL TROUGH IS NOT GOING TO
BE STRONG ENOUGH TO OVERCOME NEGATIVE INFLUENCE OF PERSISTENT MID
LEVEL RIDGE PATTERN. SO ANY ENHANCEMENT WITH THIS FEATURE OVER
PUERTO RICO-HISPANIOLA MIGHT BE SHORT IN DURATION AND VERY
LOCALIZED.

A NARROW/ELONGATED TROUGH BOUNDS THE EASTERN AND SOUTHERN FRINGES
OF THE SUBTROPICAL RIDGE TO THE WEST AND NORTH. AS THE RIDGE
BUILDS...THE TROUGH IS TO CONFINE TO THE WINDWARD ISLANDS/NORTHERN
SOUTH AMERICA WHILE GRADUALLY WEAKENING/NEARLY FILLING LATER ON
THURSDAY. AS IT MEANDERS OVER THE SOUTHERN CARIBBEAN/NORTHERN
SOUTH AMERICA...THIS IS TO ENHANCE DIURNAL CONVECTION ACROSS
NORTHWEST-NORTHERN COLOMBIA AND THE MARACAIBO REGION IN VENEZUELA.
OVER NORTHWEST-NORTHERN COLOMBIA EXPECTING RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-40MM/DAY. MAXIMA IS TO THEN PEAK AT
20-30MM/DAY THEREAFTER. ACROSS NORTHWEST VENEZUELA EXPECTING
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-30MM. THROUGH
WEDNESDAY THIS DECREASES TO 05-10MM/DAY AND MAXIMA OF 15MM.

THE SUBEQUATORIAL RIDGE IS THE DOMINANT FEATURE TO THE EAST AND
SOUTH...WITH AXIS AT 250 HPA TO EXTEND WEST ACROSS THE TROPICAL
ATLANTIC TO NORTHERN SOUTH AMERICA ALONG 05N. THE SUBTROPICAL
RIDGE LIES TO THE SOUTH... ENVELOPING MID/NORTHERN PORTIONS OF
SOUTH AMERICA. AN AREA OF DIFFLUENCE ALOFT SEPARATES THESE
RIDGES...AND THIS IS TO VENT DEEP CONVECTION ACROSS THE SOUTHERN
GUIANAS TO AMAZONIA IN SOUTHERN VENEZUELA AND COLOMBIA. IN THIS
AREA SCATTERED DEEP CONVECTION IS TO FAVOR RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-35MM. ACROSS THE NORTHERN GUIANAS TO
NORTHEAST VENEZUELA... MEANWHILE...EXPECTING RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15MM. THROUGH WEDNESDAY...AS A MOIST
PLUME ADVECTS ACROSS THE TROPICAL ATLANTIC CONVECTION IS TO
INTENSIFY...WITH RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF
15-20MM ACROSS GUYANA TO NORTHWEST SURINAME. OVER NORTHEAST
SURINAME TO FRENCH GUIANA EXPECTING HIGHER AMOUNTS WITH
ACCUMULATION OF 10-15MM/DAY AND MAXIMA OF 20-35MM LATER ON
WEDNESDAY AND INTO THURSDAY.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC
INITIAL  24     36     48     60     72     84     96        TYPE
NONE

CRAIG...TTMS (TRINIDAD AND TOBAGO)
SAMUEL...MDS (SURINAME)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)