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Tropical Discussion
 
(Latest Discussion - Issued 1524Z Apr 24, 2015)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1124 AM EDT FRI APR 24 2015

DISCUSSION FROM APRIL 24/12 UTC: AT MID/UPPER LEVELS...A HIGH
AMPLITUDE TROUGH EXTENDS FROM THE WESTERN USA TO THE TROPICAL
PACIFIC. THIS TROUGH IS PRESSING AGAINST A BUILDING RIDGE TO THE
EAST...WITH THE ENSUING GRADIENT SUSTAINING A STRONG JET PATTERN
ACROSS THE NORTHERN STATES OF MEXICO. THIS CONTINUES TO FAVOR
GENERATION OF LEE SIDE PERTURBATIONS/MOUNTAIN WAVE TURBULENCE
ACROSS NORTHWEST MEXICO. FURTHERMORE...THE DEEP TROUGH PATTERN IS
ADVECTING ITCZ MOISTURE NORTHWARD ACROSS NORTHERN MEXICO INTO THE
CENTRAL USA. THROUGH SATURDAY EVENING THE TROUGH IS TO PULL OVER
THE RIDGE TO THE EAST...WITH INFLOW OF TROPICAL MOISTURE EXPECTED
TO WANE. MEANWHILE...THIS IS TO CONTINUE FEEDING ISOLATED
CONVECTION ACROSS SINALOA-CHIHUAHUA IN WESTERN MEXICO...WHILE OVER
NORTHEAST MEXICO EXPECTING SCATTERED CONVECTION TO RESULT IN
RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM.

THE SUBTROPICAL RIDGE TO THE EAST ORIGINATES ON A CLOSED 500 HPA
HIGH OVER THE YUCATAN CHANNEL. THE RIDGE EXPANDS INTO THE CENTRAL
USA WHILE ENVELOPING SOUTHERN STATES OF MEXICO-CENTRAL AMERICA AND
MOST OF THE CARIBBEAN BASIN. ALTHOUGH RIDGE TENDS TO FLATTEN OVER
THE USA...IT IS TO REMAIN STRONG AND DOMINANT ACROSS THE CARIBBEAN
BASIN-CENTRAL AMERICA...WITH AXIS TO RAPIDLY BUILD ACROSS THE
GREATER ANTILLES TO THE NORTHEAST CARIBBEAN ISLES THROUGH
SATURDAY. THE BUILDING RIDGE PATTERN IS TO SUSTAIN A TRADE WINDS
CAP ACROSS MOST OF THE BASIN. AS THE CAP STRENGTHENS...DIURNAL
CONVECTION OVER CENTRAL AMERICA IS TO CONFINE TO SOUTHERN
GUATEMALA-SOUTHERN HONDURAS/EL SALVADOR... WHERE WE EXPECT
RAINFALL AMOUNTS OF 00-05MM/DAY AND WIDELY ISOLATED MAXIMA OF
10MM. ACROSS SOUTHERN CENTRAL AMERICA... MEANWHILE...EXPECTING
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM/DAY. THIS IS TO
INCREASE TO 05-10MM/DAY AND MAXIMA OF 15-20MM THROUGH SUNDAY
MORNING. ISOLATED CONVECTION IS ALSO EXPECTED ACROSS CENTRAL
PORTIONS OF CUBA...BUT THIS IS TO DECREASE IN COVERAGE THROUGH THE
WEEKEND UNDER THE INFLUENCE OF DEVELOPING LOW-LEVEL RIDGES. ACROSS
CENTRAL HISPANIOLA...TO CLUSTER OVER THE MOUNTAINS...EXPECT
RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM.

FARTHER EAST...AT 500 HPA...BROAD TROUGH EXTENDS ACROSS THE
WESTERN NORTH ATLANTIC. THE BROAD TROUGH IS TO SLOWLY PULL TO THE
EAST NORTHEAST THROUGH FRIDAY EVENING. LATER ON
SATURDAY...HOWEVER...THE TROUGH WILL START TO LIFT AT A FASTER
PACE AS THE AFOREMENTIONED RIDGE BUILDS TO THE SOUTH. LACKING
UPPER SUPPORT...THE ASSOCIATED FRONT IS TO STALL FAR TO THE
NORTH...WITH BOUNDARY FORECAST TO BOTTOM OUT NORTH OF THE ISLANDS
BY MIDDAY TODAY. ALTHOUGH THE FRONT REMAINS FAR TO THE
NORTH...PREFRONTAL CONVECTION ACROSS THE NORTHWEST BAHAMAS IS TO
RESULT IN RAINFALL AMOUNTS OF 00-05MM/DAY
AND MAXIMA OF 10MM THROUGH SATURDAY MORNING.

ALSO AT LOW LEVELS...THE POLAR TROUGH OVER THE WESTERN ATLANTIC
SPLITS THE SUBTROPICAL RIDGE IN TWO CELLS...WITH ONE OVER THE GULF
OF MEXICO/WESTERN CARIBBEAN AND THE OTHER OVER THE CENTRAL
ATLANTIC. AN INDUCED/INVERTED TROUGH OVER THE CENTRAL CARIBBEAN
SEPARATES THESE RIDGES TO THE SOUTH. RIDGE OVER THE GULF IS TO
WEAKEN THROUGH SUNDAY MORNING...WHILE THE ONE OVER THE CENTRAL
ATLANTIC IS TO GENERALLY PERSIST. THE LATTER IS TO ACTUALLY BECOME
BETTER ORGANIZED AS THE CYCLE PROGRESSES...BUILDING INTO THE
NORTHERN GUIANAS EARLY ON SUNDAY. AS THE RIDGE BUILDS IT IS TO
DISPLACE THE ATLANTIC ITCZ SOUTH OF ITS CLIMATOLOGICAL
POSITION...TO FAVOR A DECREASE IN CONVECTION ACROSS THE GUIANAS.
EARLY IN THE CYCLE EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-20MM ACROSS THE NORTHERN GUIANAS...WHILE OVER THE
SOUTHERN HALF EXPECTING ACCUMULATION OF 10-15MM/DAY AND MAXIMA OF
20-30MM. ACROSS THE GUIANAS THIS DECREASES TO 00-05MM/DAY AND
MAXIMA OF 10MM LATER ON SUNDAY...WITH MOST ACTIVE EXPECTED TO THE
SOUTH ALONG THE BORDER WITH BRASIL. OVER THE EASTERN CARIBBEAN THE
LOW LEVEL RIDGE IS TO SUSTAIN A SOUTH-SOUTHEASTERLY FLOW. THESE
ARE FORECAST TO PERSIST THROUGH DAY 05. EARLY IN THE CYCLE THIS
WILL FAVOR A SLIGHT INCREASE IN PWAT CONTENT ACROSS THE NORTHEAST
CARIBBEAN...BUT THIS WILL BE SHORT LASTING AS BUILDING MID LEVEL
RIDGE STRENGTHENS THE CAP INVERSION. LIGHT TRADE WIND SHOWERS ARE
EXPECTED OVER THE ISLAND CHAIN TO FAVOR TRACE RAINFALL AMOUNTS.

THE INDUCED/INVERTED LOW LEVEL TROUGH OVER THE CENTRAL CARIBBEAN
IS PHASING WITH THE PANAMANIAN LOW TO THE SOUTH. THIS IS ENHANCING
MOISTURE CONVERGENCE ALONG THE WEST COAST OF COLOMBIA. BUT THIS
WILL BE SHORT LASTING...WITH CONVECTION ON THE ANDEAN
REGION-SIERRA NEVADA DE SANTA MARTA TO PREVAIL OVER THE NEXT FEW
DAYS. IN THIS AREA EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 20-30MM THROUGH SATURDAY MORNING...WITH MAXIMA OF
15-20MM/DAY EXPECTED ON SATURDAY THROUGH MONDAY MORNING. ON THE
EASTERN PLAINS OF COLOMBIA AND CENTRAL VENEZUELA INITIALLY
EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-30MM. A
SURGE IN ACTIVITY IS EXPECTED ON SATURDAY...WITH MAXIMA TO
INCREASE TO 20-45MM...BUT ON SUNDAY IT DECREASES TO RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM.

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)