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Tropical Discussion
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
236 PM EDT THU APR 23 2015

DISCUSSION FROM APRIL 23/12 UTC: DEEP MID LEVEL TROUGH IN THE
SOUTHERN STREAM DOMINATES FLOW ACROSS THE SOUTHWEST
USA/NORTHWESTERN STATES OF MEXICO INTO THE TROPICAL PACIFIC. THIS
TROUGH IS PRESSING AGAINST BROAD CELL OF THE SUBTROPICAL RIDGE TO
THE EAST...FAVORING A TIGHT GRADIENT AND STRONG JET PATTERN ACROSS
THE NORTHERN STATES OF MEXICO. THIS IS GENERATING LEE SIDE
PERTURBATIONS/MOUNTAIN WAVE TURBULENCE. THIS TROUGH IS ALSO
ADVECTING ITCZ MOISTURE NORTH ACROSS NORTHERN MEXICO...ENHANCING
MOISTURE TRANSPORT AND CONVERGENCE ACROSS NORTHWESTERN MEXICO AND
PORTIONS OF THE SIERRA MADRE OCCIDENTAL. THROUGH FRIDAY EVENING
THE TROUGH WILL PULL TO THE NORTHEAST INTO THE SOUTHERN USA...WITH
FOCUS OF CONVERGENCE SHIFTING TO SOUTH TEXAS/RIO BRAVO.
YET...UNSTABLE SOUNDING PROFILES AND MODELS SOLUTIONS ARE
SUGGESTING THE RISK FOR SEVERE CONVECTION IN THE RIO BRAVO BASIN
LATE THURSDAY. THROUGH EARLY FRIDAY...MOISTURE CONVERGENCE OVER
SINALOA-CHIHUAHUA WILL FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND
LOCALIZED MAXIMA OF 15-25MM DECREASING VERY RAPIDLY AFTERWARDS.
ACROSS NORTHERN TAMAULIPAS-COAHUILA CONVECTION IS TO PEAK LATE
THURSDAY AND PRODUCE AMOUNTS OF 15-20MM/DAY AND ISOLATED MAXIMA OF
25-50MM/DAY WITH THE RISK OF SEVERE CONVECTION. AMOUNTS ARE TO
DECREASE AFTERWARDS AS THE MOST FAVORABLE ENVIRONMENT FOR STRONG
THUNDERSTORMS SHIFTS INTO TEXAS.

THE SUBTROPICAL RIDGE TO THE EAST EXTENDS AT MID/UPPER LEVELS
ACROSS CENTRAL/SOUTHERN MEXICO-THE GULF TO THE CENTRAL CARIBBEAN.
A 500 HPA HIGH OVER THE CAMPECHE SOUND IS TO ANCHOR THIS RIDGE
EARLY IN THE CYCLE...WITH CLOSED HIGH TO DRIFT EAST TO THE WESTERN
CARIBBEAN EARLY THIS WEEKEND. AS THE HIGH RELOCATES THE RIDGE IS
TO BUILD EAST ACROSS THE NORTHERN CARIBBEAN ISLANDS...TO RAPIDLY
ENVELOP MOST OF THE BASIN AND NORTHERN PORTIONS OF
COLOMBIA/VENEZUELA. THE BUILDING RIDGE PATTERN IS TO FAVOR A TRADE
WINDS CAP ACROSS MOST OF THE BASIN...WITH DIURNAL CONVECTION OVER
CENTRAL AMERICA TO CONFINE TO SOUTHERN GUATEMALA-SOUTHERN
HONDURAS/EL SALVADOR...WHERE WE EXPECT RAINFALL AMOUNTS OF
00-05MM/DAY AND MAXIMA OF 10MM. OVER SOUTHERN CENTRAL AMERICA
EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF
15-25MM/DAY THROUGH EARLY FRIDAY...DECREASING RAPIDLY AFTERWARDS.
OTHER CONVECTION IS EXPECTED ACROSS CENTRAL PORTIONS OF CUBA TO
PRODUCE MAXIMA OF 10MM/DAY...GRADUALLY DECREASING IN COVERAGE
THROUGH THE WEEKEND UNDER THE INFLUENCE OF DEVELOPING LOW-LEVEL
RIDGES.

EAST OF THE RIDGE...POLAR TROUGH EXTENDS ACROSS THE EASTERN USA TO
THE WESTERN ATLANTIC...WITH BROAD TROUGH 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 RIDGE BUILDS TO THE SOUTH. LACKING UPPER SUPPORT...THE
ASSOCIATED FRONT IS TO STALL FAR TO THE NORTH...WITH BOUNDARY TO
BOTTOM OUT NORTH OF THE ISLANDS BY MIDDAY ON FRIDAY. ALTHOUGH IT
IS TO REMAIN 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...DECREASING AFTERWARDS.

LOW LEVEL RIDGE OVER THE CENTRAL ATLANTIC IS TO YIELD TO
AMPLIFYING TROUGH OVER THE WESTERN ATLANTIC. AS THE RIDGE PULLS
AWAY...LOW LEVEL WINDS OVER THE EASTERN CARIBBEAN WILL SHIFT TO
THE SOUTH-SOUTHEAST. EARLY IN THE CYCLE THIS WILL FAVOR A SLIGHT
INCREASE IN PWAT AMOUNTS ACROSS THE NORTHEAST CARIBBEAN...BUT THIS
WILL BE SHORT LASTING AS BUILDING MID LEVEL RIDGE STRENGTHENS THE
CAP INVERSION. EARLY IN THE CYCLE TRADE WIND SHOWERS OVER THE
ISLAND CHAIN ARE TO FAVOR TRACE AND ISOLATED RAINFALL AMOUNTS.

MID LEVEL RIDGE TO THE WEST IS TO ALSO STEER A SHORT WAVE TROUGH
ACROSS THE BAHAMAS TO HISPANIOLA EARLY IN THE CYCLE...TO REACH
PUERTO RICO DURING EARLY MORNING HOURS ON FRIDAY. WEAK DIVERGENCE
ALOFT IS TO PRECEDE WAVE PASSAGE...WITH SOME ENHANCEMENT OF
DIURNAL CONVECTION POSSIBLE ACROSS CENTRAL PORTIONS OF HISPANIOLA
EARLY THIS AFTERNOON...TO FAVOR RAINFALL AMOUNTS OF 00-05MM/DAY
AND MAXIMA OF 10MM. ISOLATED HIGHER AMOUNTS ARE POSSIBLE IN
INTERACTION WITH OROGRPAHY. SIMILARLY ACROSS PUERTO RICO...WHERE
DIVERGENT PATTERN ALOFT IS TO RESULT IN VERY LIGHT RAINFALL
AMOUNTS.

FARTHER SOUTH...THE SUBEQUATORIAL RIDGE EXTENDS WEST ACROSS THE
TROPICAL ATLANTIC TO NORTHERN SOUTH AMERICA...WITH 250 HPA AXIS
ORIGINATING ON A CLOSED HIGH NEAR 03N 35W. THE RIDGE ALOFT IS
VENTING CONVECTION ACROSS THE GUIANAS...WITH RAINFALL MAXIMA OF
20-35MM/DAY OVER SURINAME AND FRENCH GUIANA...AND MAXIMA OF
15-25MM/DAY WEST OVER NORTHERN GUYANA AND NORTHEASTERN VENEZUELA
THROUGH EARLY FRIDAY. THE BUILDING SUBTROPICAL RIDGE TO THE WEST
IS TO STRENGTHEN THE CAP INVERSION TO THE NORTH AND WEST...LEADING
TO GRADUAL EROSION OF AVAILABLE WATER AND DECREASE IN ACTIVITY
OVER THE GUIANAS AFTERWARDS.

THE SUBEQUATORIAL RIDGE IS ALSO VENTING CONVECTION ACROSS COLOMBIA
AND VENEZUELA...WITH ACTIVITY OVER COLOMBIA CLUSTERING OVER THE
ANDES. IN THIS AREA EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND
MAXIMA OF 20-35MM DECREASING TO MAXIMA OF 15-20MM/DAY DURING
SATURDAY INTO SUNDAY. ON THE EASTERN PLAINS OF COLOMBIA AND
CENTRAL VENEZUELA INITIALLY EXPECTING RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-35MM. THESE ARE TO INCREASE TO MAXIMA
OF 20-45MM/DAY BY SATURDAY INTO EARLY SUNDAY.

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)