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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1815Z Apr 17, 2015)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
215 PM EDT FRI APR 17 2015

DISCUSSION FROM APRIL 17/12 UTC: WEST OVER THE DOMAIN...A
MID/UPPER LEVEL TROUGH EXTENDS OVER THE SOUTHWEST USA TO THE
NORTHERN STATES OF MEXICO... WITH AXIS PRESSING AGAINST A RIDGE TO
THE EAST AND SOUTH. THROUGH SATURDAY EVENING/EARLY SUNDAY MORNING
THE TROUGH IS TO PULL TO THE EAST-NORTHEAST. AS IT PULLS AWAY...A
MORE ZONAL WESTERLY FLOW IS TO ESTABLISH ACROSS MEXICO INTO THE
NORTHERN GULF. EARLY IN THE CYCLE THE INFLOW OF SHORT WAVE ENERGY
WILL ENHANCE CONVECTIVE DEVELOPMENT ACROSS THE NORTHEAST STATES OF
MEXICO...WITH MOST ACTIVE CLUSTERING ALONG THE SIERRA MADRE
OCCIDENTAL. IN THIS AREA EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY
AND MAXIMA OF 15-25MM. THROUGH SUNDAY THIS WILL DECREASE TO
00-05MM/DAY AND MAXIMA OF 10MM.

MID LEVEL RIDGE TO THE EAST IS TO INITIALLY CENTER ON A CLOSED
HIGH OVER THE NORTHERN YUCATAN...WITH AXIS ENVELOPING THE GULF OF
MEXICO-SOUTHERN STATES OF MEXICO-MOST OF CENTRAL AMERICA AND THE
GREATER ANTILLES WEST OF HISPANIOLA. THROUGH SUNDAY EVENING THE
RIDGE IS TO FLATTEN AS THE AFOREMENTIONED TROUGH LIFTS OVER THIS
AXIS. LATER DURING THE WEEKEND A NARROW/ELONGATED RIDGE IS TO
CONFINE TO THE NORTHWEST CARIBBEAN. AS THE RIDGE WEAKENS CAP
INVERSION OVER CENTRAL AMERICA-SOUTHERN STATES OF MEXICO IS
EXPECTED TO WEAKEN. THIS...IN-TURN...IS TO FAVOR AN INCREASE IN
DIURNAL CONVECTION ALONG THE CONTINENTAL DIVIDE BETWEEN THE
SOUTHERN STATES OF MEXICO TO HONDURAS/EL SALVADOR. IN THIS AREA
INITIALLY EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF
10MM. THIS INCREASES TO 05-10MM/DAY AND MAXIMA OF 15-20MM LATER ON
SUNDAY AFTERNOON/EVENING. ACROSS CUBA DIURNAL CONVECTION IS TO
SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM
THROUGH SATURDAY. THIS DECREASES TO 00-05MM/DAY AND MAXIMA OF 10MM
ON SUNDAY TO MONDAY. OVER JAMAICA AND CENTRAL PORTIONS OF
HISPANIOLA EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF
10MM.

SHORT WAVE PERTURBATIONS LIFTING OVER THE MID/UPPER LEVEL RIDGE
ARE TO STREAM ACROSS THE SOUTHERN USA WHILE REMAINING TO THE NORTH
OF THE BAHAMAS. AT LOW LEVELS THIS WILL SUSTAIN A BAROCLINIC
BOUNDARY OVER THE WESTERN ATLANTIC INTO THE EASTERN USA. ALTHOUGH
BOUNDARY REMAINS FAR TO THE NORTH...INFLOW OF SHORT WAVE ENERGY
ALOFT AND PROXIMITY OF THE SURFACE FRONT MIGHT BE ENOUGH TO ALLOW
FOR SOME CONVECTION TO DEVELOP ACROSS GREAT ABACO-GRAND BAHAMA
OVER THE NEXT COUPLE OF DAYS...WITH RAINFALL AMOUNTS OF
00-05MM/DAY AND MAXIMA OF 10MM EXPECTED THROUGH SATURDAY.

DOWNSTREAM FROM THE WESTERN CARIBBEAN/CENTRAL AMERICA RIDGE...A
MID/UPPER LEVEL TROUGH EXTENDS ACROSS THE EASTERN CARIBBEAN TO
NORTHERN VENEZUELA. AT 250 HPA A SUBTROPICAL JET MAXIMA BOUNDS THE
SOUTHERN FRINGES OF THIS TROUGH...WITH AXIS NORTHEAST FROM NEAR
THE ABC ISLES...ACROSS THE FRENCH ISLANDS INTO THE TROPICAL
ATLANTIC. JET MAXIMA IS FORECAST TO GRADUALLY PULL TO THE
EAST-NORTHEAST THROUGH SATURDAY EVENING. AS THE JET PULLS AWAY...
CONVERGENCE OVER THE NORTHEAST CARIBBEAN ISLES IS TO
WEAKEN...WHILE NEUTRAL TO DIVERGENT CONDITIONS PREVAIL OVER THE
SOUTHEAST CARIBBEAN-NORTHERN SOUTH AMERICA. ALTHOUGH JET PULLS
AWAY...A MID/UPPER LEVEL SHORT WAVE TROUGH IS TO REMAIN OVER THE
EASTERN CARIBBEAN ISLES...AND THIS IS TO CONTINUE ENHANCING
SHALLOW LAYER CONVECTIVE INSTABILITY OVER THE EASTERN CARIBBEAN
THROUGH MONDAY MORNING. AT LOW LEVELS...BROAD RIDGE EXTENDS ACROSS
THE CENTRAL ATLANTIC TO THE NORTHERN CARIBBEAN ISLES.
AFOREMENTIONED POLAR TROUGH OVER THE WESTERN ATLANTIC IS TO PRESS
AGAINST THIS AXIS...WITH HIGH/RIDGE TO GRADUALLY RELOCATE TO THE
EAST-NORTHEAST EARLY ON SATURDAY. AS THE HIGH RELOCATES AND THE
PRESSURE GRADIENT SLACKENS THE PREVAILING EASTERLY TRADES OVER THE
BASIN ARE TO WEAKEN. THIS...IN-TURN...WILL ALLOW FOR DEEPER
MOISTURE TO POOL ACROSS THE ISLAND CHAIN-NORTHEAST CARIBBEAN
ISLES...WHERE PWAT IS TO PEAK AT 25-30MM OVER THE NEXT THREE DAYS.
ACROSS THE ISLAND CHAIN THIS IS TO HELP SUSTAIN SCATTERED
CONVECTION WITH ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-20MM.
MOST ACTIVE IS FORECAST TO CLUSTER ACROSS THE WINDWARD AND
NORTHERN LEEWARD ISLANDS THROUGH SATURDAY MORNING. THIS THEN
DECREASES TO 00-05MM/DAY AND MAXIMA OF 10MM IN ISOLATED TO
SCATTERED CONVECTION. OVER PUERTO RICO...DIURNAL CONVECTION IS TO
FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM
THROUGH SATURDAY EVENING...DECREASING TO 05-10MM/DAY AND MAXIMA OF
15MM ON SUNDAY.

ALSO AT 250 HPA...THE SUBEQUATORIAL RIDGE EXTENDS WEST ACROSS THE
TROPICAL ATLANTIC ALONG 05N...THE GUIANAS-SOUTHERN VENEZUELA TO
COLOMBIA. THIS IS VENTING DEEP CONVECTION ALONG THE ITCZ INTO
EQUATORIAL SOUTH AMERICA. EMBEDDED IN THIS FLOW A WEAK
PERTURBATION IN THE EASTERLY TRADES MOVES ACROSS THE GUIANAS EARLY
IN THE CYCLE...AND ACROSS VENEZUELA THROUGH THE  AFTERNOON HOURS
ON SATURDAY...REACHING COLOMBIA ON SUNDAY. MOIST PLUME ASSOCIATES
WITH THIS FEATURE...ENHANCING CONVECTION ACROSS THE GUIANAS EARLY
IN THE CYCLE. IN THIS AREA EXPECTING RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-30MM. THIS THEN DECREASES TO
00-05MM/DAY AND MAXIMA OF 10MM THROUGH SUNDAY. ACROSS VENEZUELA IT
IS TO FAVOR RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 25-50MM
THROUGH SATURDAY...DECREASING TO 10-15MM/DAY AND MAXIMA OF
20-35MM. AS IT ENTERS COLOMBIA...RAINFALL AMOUNTS INCREASE TO
15-20MM/DAY AND MAXIMA OF 25-50MM ON SUNDAY.

THE RIDGE ALOFT IS TO ALSO ENHANCE DIURNAL CONVECTION ACROSS
COLOMBIA...WITH ACTIVITY TO SPLIT BETWEEN THE ANDEAN REGION AND
THE EASTERN PLAINS. ON THE CAUCA-CAUCA VALLEY AND SOUTHWEST STATES
OF COLOMBIA EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA
OF 20-40MM THROUGH SATURDAY...WHILE OVER NORTHWEST-NORTHERN
COLOMBIA EXPECTING ACCUMULATION OF 15-20MM/DAY AND MAXIMA OF
25-50MM. ON SATURDAY THIS DECREASES TO 10-15MM/DAY AND MAXIMA OF
20-35MM. ON THE EASTERN PLAINS OF COLOMBIA DIURNAL CONVECTION IS
TO FAVOR RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 25-50MM. ON
SUNDAY THIS DECREASES TO 10-15MM/DAY AND MAXIMA OF 20-35MM.

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)