Prognostic Meteorological Discussion
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FXCA20 KWBC 201823
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
222 PM EDT FRI OCT 20 2017

TROPICAL DISCUSSION FROM OCT 20/12 UTC: THE GFS...CFS AND
EMPIRICAL WAVE PROPAGATION MODELS OF CPC ARE SUGGESTING THAT THE
UPPER DIVERGENT PHASE OF THE MADDEN-JULIAN OSCILLATION WILL
ESTABLISH OVER THE AMERICA SURING THE WEEKEND INTO EARLY NEXT
WEEK. THIS WILL ENHANCE ANY CONVECTIVE ACTIVITY AND PRECIPITATION
THAT DEVELOPS IN THE REGION DURING THE LAST 10 DAYS OF OCTOBER.

STRONG POLAR EXITING THE EAST COAST OF THE UNITED STATES CONTINUES
INTERACTING WITH A SURFACE FRONT THAT IS FORECAST TO LIGER TO THE
NORTH OF THE BAHAMAS THROUGH THE CYCLE...AS WELL AS WITH A SURFACE
TROUGH THAT IS TO MEANDER  AHEAD OF THE FRONT IN THE BAHAMAS. THE
DYNAMICAL ENHANCEMENT OF ASCENT IN ASSOCIATION WITH THE
APPROACHING UPPER TROUGH IS TO PEAK ON FRIDAY...TO THEN MOVE
SOUTHEASTWARD. THIS WILL LEAD TO A PEAK IN ACCUMULATIONS ON
FRIDAY-SATURDAY...WHEN EXPECTING 05-10MM/DAY AND ISOLATED MAXIMA
OF 15-25MM IN THE CENTRAL BAHAMAS...DECREASING TO 00-05MM/DAY AND
MAXIMA OF 10MM AFTER.

OTHER FEATURE OF INTEREST IS A TRADE WIND SURGE THAT IS
PROPAGATING ACROSS THE CENTRAL CARIBBEAN. THIS SURGE IS
ACCOMPANIED BY A SUBSIDENCE CAP THAT SITS AT 900 HPA...BY TRADE
WINDS IN THE 20-30KT RANGE...AND BY VERY DRY MID-LEVELS.
ACCORDINGLY...ONCE THE TRADE WIND SURGE CROSSES A
LOCATION...EXPECTING A SHARP DECREASE IN RAINFALL ACCUMULATIONS.
ON FRIDAY EVENING THE SURGE EDGE WILL EXTEND ACROSS HAITI...BY
SATURDAY EVENING JUST WEST OF JAMAICA...AND BY SUNDAY EVENING JUST
TO THE WEST OF THE CAYMAN ISLANDS. BY THIS TIME THE SURGE WILL
START LOSING DEFINITION. AHEAD OF THE SURGE...PRECIPITATION IS
BEING STIMULATED BY ENHANCED TRADE WIND CONVERGENCE...BUT ALSO BY
A TROPICAL WAVE. THIS WILL INITIALLY LEAD TO 10-15MM/DAY AND
MAXIMA OF 20-35MM IN JAMAICA...ALTHOUGH STRONGEST ACTIVITY IS
FORECAST TO REMAIN OFFSHORE. BY SATURDAY-SUNDAY...TROPICAL WAVE
CONVECTION WILL ENHANCE ACTIVITY IN NORTHEASTERN HONDURAS AND
EASTERN NICARAGUA. NOTE THAT MOISTURE CONVERGENCE WILL BE
REINFORCED BY THE CONVERGENCE IN THE MOUTH OF A LOW-LEVEL JET.
THIS WILL SUSTAIN ACCUMULATIONS OF 15-30MM/DAY AND MAXIMA OF
40-80MM...THAT ARE TO EXTEND INTO NORTHERN HONDURAS/EASTERN
GUATEMALA AND SOUTHERN BELIZE. BY SUNDAY-MONDAY...LARGEST
ACCUMULATIONS ARE EXPECTED IN BELIZE/NORTHERN GUATEMALA AND
SOUTHERN MEXICO. DURING THIS PERIOD...THE TROPICAL WAVE WILL
INTERACT WITH A DEVELOPING NORTHERLY SURGE AND A SHEAR LINE IN THE
GULF OF MEXICO. THIS WILL LEAD TO 25-50MM/DAY AND MAXIMA OF
75-125MM. LARGER ACCUMULATIONS ARE EXPECTED ON MONDAY-TUESDAY IN
SOUTHERN MEXICO/NORTHERN GUATEMALA.

REGARDING THE SURGE IN THE GULF OF MEXICO BY THE LATE
WEEKEND...THE ASSOCIATED SURFACE FRONT IS FORECAST TO EXTEND INTO
SOUTHERN TEXAS BY SUNDAY EVENING...AND INTO CENTRAL
VERACRUZ-MEXICO BY MONDAY EVENING. THE SHEAR LINE WILL FORM ON
SUNDAY...AND BY SUNDAY EVENING IT WILL EXTEND FROM SOUTHERN
LOUISIANA INTO THE GULF OF CAMPECHE...AND BY MONDAY EVENING THE
SHEAR LINE WILL EXTEND ACROSS THE YUCATAN CHANNEL INTO WESTERN
BELIZE/CENTRAL GUATEMALA. THIS WILL REINFORCE THE AFOREMENTIONED
WET SPELL IN THE REGION...TO SUSTAIN LARGEST ACCUMULATIONS BETWEEN
SUNDAY AND TUESDAY.

IN SOUTHERN CENTRAL AMERICA...ACTIVE CONVECTION IS TO PERSIST
THROUGH THE CYCLE UNDER THE INFLUENCE OF A MOISTURE POOL THAT
EXCEEDS 60MM...AND A MODERATELY ORGANIZED PANAMANIAN LOW. THIS
WILL SUSTAIN ACCUMULATIONS OF 10-15MM/DAY AND MAXIMA OF 20-40MM IN
COSTA RICA AND WESTERN PANAMA ON A DAILY BASIS. LESSER AMOUNTS ARE
EXPECTED IN EASTERN PANAMA. NOTE THAT THE ITCZ IS FORECAST TO
MEANDER IN THE SOUTHERN CARIBBEAN THROUGH THE CYCLE. A SYSTEM OF
INTEREST IS A BROAD LOW ORGANIZING IN THE REGION DURING
MONDAY-TUESDAY. THIS WILL SUSTAIN ENHANCED SOUTHWESTERLY WINDS
ACROSS THE PACIFIC BASINS OF WESTERN PANAMA AND WESTERN COSTA
RICA. THIS WILL LEAD TO EXTREME MOISTURE CONVERGENCE...WHICH WILL
LIKELY SUSTAIN RAINFALL ACCUMULATIONS OF 100-200MM/DAY ON SOUTHERN
COSTA RICA AND WESTERN PANAMA ON THE TUESDAY-EARLY WEDNESDAY TIME
FRAME. NOTE THAT THE MODELS ARE DIVERGING WITH THE STRENGTH AND
LOCATION OF THE AREAS OF STRONGEST MOISTURE CONVERGENCE AND
RAINFALL. THE GFS IS THE MOST AGGRESSIVE...AS IT SUGGESTS MAXIMA
OF 200-300MM/DAY...WHILE THE UKMET IS THE MOST CONSERVATIVE...AS
IT SUGGESTS MAXIMA OF 100-150MM/DAY.

IN NORTHERN SOUTH AMERICA AND THE SOUTHERN CARIBBEAN...ITCZ
CONVERGENCE WILL CONTINUE SUSTAINING MODERATE ACCUMULATIONS IN
TRINIDAD AND TOBAGO/NORTHEASTERN VENEZUELA...ALTHOUGH AMOUNTS ARE
DECREASING. THROUGH EARLY SATURDAY EXPECTING 10-15MM/DAY AND
MAXIMA OF 20-40MM. THIS IS DECREASING TO 10-15MM/DAY AND MAXIMA OF
20-30MM AFTER. TRANSIENT WET PATTERN IS ALSO EXPECTED IN THE ABC
ISLANDS...WHERE MOISTURE PLUME TO THE SOUTH OF THE CARIBBEAN
LOW-LEVEL JET WILL SUSTAIN ACCUMULATIONS OF 05-10MM/DAY AND MAXIMA
OF 15-20MM/DAY THROUGH EARLY SUNDAY...DECREASING AFTER. ANOTHER
REGION OF INTEREST IS COLOMBIA...WHERE ACTIVE SEASONAL CONVECTION
IS BEING REINFORCED BY ENHANCED WESTERLIES ACROSS THE PACIFIC
BASIN. THIS WILL SUSTAIN ACCUMULATIONS OF 15-20MM/DAY AND MAXIMA
OF 25-50MM IN WESTERN COLOMBIA ON FRIDAY...WHILE IN
CENTRAL/NORTHERN COLOMBIA EXPECTING 10-15MM/DAY AND MAXIMA OF
20-35MM. BY SATURDAY AND INTO MONDAY THIS INCREASES TO 15-20MM/DAY
AND MAXIMA OF 35-70MM...WHILE IN NORTHERN COLOMBIA EXPECTING
10-15MM/DAY AND MAXIMA OF 20-40MM.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:
INITIAL   24    36    48    60    72    84    96   TYPE  SOF
41W      43W   45W   48W   52W   55W   58W   61W   TW    20N
77W      80W   82W   84W   87W   89W   90W   91W   TW    19N
94W      DISSIPATES                                TW    22N

A TROPICAL WAVE INITIALIZED AT 41W WILL ARRIVE INTO THE GUIANAS ON
EARLY MONDAY. ENHANCED TRADE WIND CONVERGENCE AHEAD OF THE WAVE
AXIS WILL SUSTAIN AN INCREASE IN ACCUMULATIONS TO 10-15MM/DAY AND
MAXIMA OF 20-30MM.

TROPICAL WAVE INITIALIZED AT 77W WILL HAVE A SIGNIFICANT IMPACT IN
PRECIPITATION AS IT PROPAGATES INTO CENTRAL AMERICA DURING
SATURDAY-MONDAY (SEE ABOVE FOR ACCUMULATIONS). IN THE MEAN
TIME...THE WAVE WILL ENHANCE AMOUNTS IN JAMAICA ON FRIDAY...WHERE
IT WILL SUSTAIN MAXIMA OF 20-35MM...MOSTLY OFFSHORE.

A TROPICAL WAVE INITIALIZED AT 94W HAS LOST DEFINITION.

GUY...NMS (BELIZE)
PECK...MS (JAMAICA)
GALVEZ...WPC (USA)
$$




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