Prognostic Meteorological Discussion
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FXCA20 KWBC 181921
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM EST WED JAN 18 2017

TROPICAL DISCUSSION FROM JAN 18/12 UTC: MID/UPPER LEVEL RIDGE
EXTENDS NORTH FROM CENTRAL AMERICA/WESTERN CARIBBEAN TO THE
EASTERN USA. THE RIDGE IS TO GENERALLY HOLD DURING THE NEXT FEW
DAYS...MEANWHILE ANCHORING AT 500 HPA HIGH THAT IS TO MEANDER OVER
THE NORTHWEST CARIBBEAN. THE RIDGE SUSTAINS A FAIRLY STRONG CAP
INVERSION ACROSS THE BAHAMAS-GREATER ANTILLES AND MOST OF CENTRAL
AMERICA/THE SOUTHERN STATES OF MEXICO. THE STRONG CAP INVERSION
WILL FAVOR FAIR WEATHER CONDITIONS ACROSS THE BAHAMAS-GREATER
ANTILLES AND MOST OF CENTRAL AMERICA. TRADE WIND CONVERGENCE WILL
LIMIT TO EASTERN NICARAGUA AND BELIZE...WHERE WE EXPECT RAINFALL
AMOUNTS OF 00-05MM/DAY AND ISOLATED MAXIMA OF 10MM. ON FRIDAY TO
SATURDAY THE CAP OVER THE SOUTHERN CARIBBEAN WILL WEAKEN ENOUGH TO
ALLOW FOR SLIGHT INCREASE IN DIURNAL CONVECTION OVER WESTERN
PANAMA AND COSTA RICA...TO SUSTAIN RAINFALL AMOUNTS OF 00-05MM/DAY
AND MAXIMA OF 10MM.

AS THE MID/UPPER LEVEL RIDGE HOLDS...A TROUGH OVER THE WESTERN USA
IS TO GRADUALLY LIFT OVER THIS AXIS. THIS IS TO PULL ACROSS
SONORA/SINALOA TO ARIZONA/NEW MEXICO IN THE SOUTHWEST USA LATER
THIS AFTERNOON...AND THEN EAST ACROSS THE MISSISSIPPI VALLEY ON
THURSDAY EVENING. AS IT PULLS ACROSS NORTHERN MEXICO THIS TROUGH
WILL SUSTAIN A SUBTROPICAL CONNECTION...FOCUSING MOISTURE ACROSS
SOUTHWEST-NORTHEAST MEXICO. MOIST INFLOW IS TO FAVOR SCATTERED
CONVECTION BETWEEN SOUTHERN SINALOA AND COLIMA/NAYARIT...WITH
RAINFALL AMOUNTS 00-05MM/DAY AND MAXIMA OF 10MM. OTHER CONVECTION
IS TO CLUSTER TO THE NORTH ALONG THE RIO BRAVO BETWEEN COAHUILA
AND TAMAULIPAS...WITH SIMILAR RAINFALL AMOUNTS THROUGH FRIDAY
MORNING.

NEXT POLAR TROUGH IS TO ENTER WESTERN USA/NORTHWEST MEXICO LATER
ON THURSDAY...TO GRADUALLY MOVE INTO NORTHERN MEXICO ON FRIDAY
EVENING. THIS IS TO ALSO ENHANCE MOISTURE CONVERGENCE ON THE
NORTHWEST STATES OF MEXICO LATER ON THURSDAY... TRIGGERING
SCATTERED CONVECTION OVER NORTHERN BAJA PENINSULA WITH
ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-20MM. ON FRIDAY THIS
INCREASES TO 10-15MM/DAY AND MAXIMA OF 20-35MM WHILE SPREADING
EAST ACROSS SONORA TO WESTERN CHIHUAHUA. DURING THAT PERIOD
ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE AND CONDUCIVE FOR SNOW
SHOWERS TO DEVELOP ON WESTERN PORTIONS OF CHIHUAHUA...TO FAVOR
SNOWFALL AMOUNTS OF 15-25CM. THIS IS TO ALSO FAVOR FRONTOGENESIS
OVER TEXAS LATER ON SATURDAY...WITH BOUNDARY TO SURGE ACROSS THE
NORTHWEST GULF/NORTHEAST STATES OF MEXICO EARLY ON SUNDAY MORNING.
MOST ACTIVE CONVECTION...HOWEVER...IS EXPECTED TO THE NORTH OVER
THE USA.

AS THE MID/UPPER LEVEL RIDGE HOLDS OVER THE EASTERN USA...IT IS TO
STEER SHORT WAVE PERTURBATIONS ACROSS THE WESTERN ATLANTIC/NORTH
OF THE ISLANDS. IN THIS PATTERN... A PROGRESSIVE PERTURBATION IS
TO STREAM ACROSS THE BAHAMAS EARLY ON FRIDAY MORNING...TO REACH
THE NORTHEAST CARIBBEAN ISLES LATER IN THE DAY. THE INFLOW OF
SHORT WAVE ENERGY IS TO THEN FAVOR SOUTHWARD AMPLIFICATION OF A
LONG WAVE TROUGH BETWEEN 70W-45W AND TO THE NORTH OF 14N. THIS
HOWEVER...WILL BE SHORT LIVED...WITH TROUGH TO QUICKLY PULL TO THE
NORTHEAST ON FRIDAY. THIS SETS THE STAGE FOR A DEEPER/STRONGER
PERTURBATION TO FOLLOW. THE LATTER MOVES OVER THE BAHAMAS ON
FRIDAY EVENING...REACHING THE NORTHEAST CARIBBEAN ISLES EARLY ON
SATURDAY MORNING. THE TROUGH REACHES MAXIMUM AMPLITUDE LATER ON
SATURDAY/EARLY SUNDAY MORNING WHILE MEANDERING EAST OF THE LESSER
ANTILLES. AT LOW LEVELS...BROAD RIDGE IS INITIALIZED OVER THE
WESTERN ATLANTIC/NORTH OF THE GREATER ANTILLES. POLAR FRONTS
EXITING THE EASTERN USA ARE TO PRESS AGAINST THIS AXIS...LEADING
TO RAPID EROSION/WEAKENING OF THE RIDGE DURING THE DAY TODAY. AS
THE RIDGE WEAKENS AND PRESSURE GRADIENT SLACKENS LIGHTER TRADES
ARE TO ENVELOP THE ENTIRE BASIN. THIS WILL COMBINE WITH STRONG
TRADE WINDS CAP ACROSS THE BASIN TO GENERALLY FAVOR FAIR WEATHER
CONDITIONS. THIS PATTERN WILL HOLD DURING THE NEXT THREE DAYS.
DURING THE WEEKEND...A WANING FRONT MEANDERS SOUTH TOWARDS THE
NORTHERN CARIBBEAN ISLES...WHERE IT IS TO FAVOR A SLIGHT INCREASE
IN LOW LEVEL MOISTURE...BRINGING LIGHT CONVECTION TO NORTHERN
HISPANIOLA-PUERTO RICO...WITH RAINFALL AMOUNTS OF 00-05MM/DAY AND
MAXIMA OF 10MM.

A LOW LEVEL RIDGE WILL THEN ROLL FROM THE WEST ACROSS FLORIDA/CUBA
TO THE WESTERN ATLANTIC...WITH LOW LEVEL WINDS BACKING TO THE
NORTH-NORTHWEST. THE RIDGE PATTERN IS TO GRADUALLY STRENGTHEN
DURING THE WEEKEND. THIS IS TO THEN FAVOR A PREFRONTAL SHEAR LINE
ACROSS THE WINDWARD ISLANDS TO NORTHERN VENEZUELA ON FRIDAY TO
SATURDAY. UNDER INFLUENCE OF THIS FEATURE EXPECTING CONVECTIVE
ACTIVITY TO INCREASE FROM 00-05MM/DAY AND MAXIMA OF 10MM/DAY TODAY
AND TOMORROW TO 10-15MM/DAY MAXIMA OF 20-35MM/DAY ON FRIDAY AND
SATURDAY. AS A SLOW TO EVOLVE FEATURE...THIS COULD LEAD TO AN ECHO
TRAINING PATTERN OVER THE WINDWARD ISLES...WITH RISK FOR EXCESSIVE
RAINFALL AMOUNTS ACROSS BARBADOS-GRENADINES.

THE WESTERN CARIBBEAN RIDGE IS TO ALSO STEER A MID LEVEL TROUGH
ACROSS COLOMBIA TO ECUADOR EARLY IN THE CYCLE. THIS EVOLVES INTO A
CLOSED LOW WEST OF ECUADOR LATER TODAY...WITH AXIS TO DRIFT SOUTH
OF THE GALAPAGOS ISLANDS LATER ON THURSDAY. THE MID LEVEL VORTEX
IS TO INTERACT WITH THE EASTERN PACIFIC ITCZ OVER SOUTHWEST
COLOMBIA TO TRIGGER SCATTERED DEEP CONVECTION...WITH RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM OVER THE NEXT COUPLE
OF DAYS. ON FRIDAY TO SATURDAY CONDITIONS APPEAR CONDUCIVE FOR
ORGANIZED HEAVY CONVECTION TO DEVELOP ACROSS ECUADOR AND THE CAUCA
VALLEY...WITH RAINFALL AMOUNTS FO 20-40MM/DAY AND MAXIMA OF
50-100MM. ON THE EJE CAFETERO TO THE NORTHWEST...THIS WILL
INCREASE TO 10-15MM/DAY AND MAXIMA OF 20-30MM. ACROSS SOUTHERN
VENEZUELA AND AMAZONIA IN COLOMBIA EXPECTING SCATTERED CONVECTION
WITH ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-25MM/DAY. ON
FRIDAY TO SATURDAY THIS INCREASES TO 10-15MM/DAY AND MAXIMA OF
20-35MM. OVER THE GUIANAS...AS ENHANCED BY MID/UPPER LEVEL TROUGH
OVER THE CENTRAL ATLANTIC... EXPECTING RAINFALL AMOUNTS OF
05-10MMD/AY AND MAXIMA OF 15-25MM/DAY.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:

INITIAL   24     36     48     60     72     84     96    TYPE
NONE

JIMENEZ...IMN (COSTA RICA)
MIRANDA...INAMEH (VENEZUELA)
DAVISON...WPC (USA)

$$




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