509
FXCA20 KWBC 011910
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
310 PM EDT THU OCT 01 2026
FORECAST BULLETIN 1 OCTOBER 2026 AT 1900 UTC:
THE SUBTROPICAL JET STREAM EXTENDS OVER THE NORTHERN MEXICAN
STATES TODAY, INTERACTING WITH AN UPPER-LEVEL TROUGH OVER THE
CENTRAL-WESTERN US AND A RIDGE EXTENDING FROM WESTERN MEXICO INTO
THE NORTHWESTERN GULF. THIS PATTERN IS EXPECTED TO PERSIST OVER
THE REGION FOR THE NEXT FEW DAYS, INTERACTING WITH A COUPLE OF
SHORTWAVES WHILE FAVORING UPPER-LEVEL DIVERGENCE OVER THE NORTHERN
MEXICAN ALTIPLANO AND NORTHERN SIERRA MADRE ORIENTAL. OFF WESTERN
MEXICO, HURRICANE RACHEL'S UPPER-LEVEL CIRCULATION INTERACTS WITH
THE SOUTHERN FLANK OF THE UPPER-LEVEL JET STREAM TO ENHANCE
UPPER-LEVEL DIVERGENCE FROM SINALOA INTO THE ALTIPLANO TODAY. IN
THE MID-LEVELS, POSITIVE POTENTIAL VORTICITY WILL ENHANCE OVER THE
MEXICAN ALTIPLANO, SUPPORTING AREAS OF STRONG UPWARD MOTION.
MID-TO-LOW-LEVEL FLOW WILL SUPPORT HIGH MOISTURE TRANSPORT FROM
THE PACIFIC INTO WESTERN AND CENTRAL MEXICO TODAY AND IS EXPECTED
TO SHIFT TO EASTERLY FLOW OVER THE COMING DAYS, SUSTAINING
MID-LEVEL MOISTURE AVAILABILITY. WIDESPREAD HEAVY PRECIPITATION IS
FORECAST TODAY ACROSS THE MEXICAN ALTIPLANO TO THE NORTHERN SIERRA
MADRE ORIENTAL, WHERE IT WILL LINGER FOR THE NEXT THREE DAYS WHILE
BECOMING MORE ISOLATED TO THE WEST.
AN UPPER-LEVEL CUT-OFF LOW CENTERED OVER TABASCO WILL SUSTAIN
STRONG UPPER-LEVEL WIND DIVERGENCE OVER CENTRAL TO SOUTHWESTERN
MEXICO, FROM TABASCO TO GUATEMALA, AND FROM THE YUCATAN PENINSULA
TO THE BAHAMAS TODAY. A WELL-DEFINED AREA OF POSITIVE POTENTIAL
VORTICITY OVER THESE REGIONS WILL SUPPORT ENHANCED UPWARD MOTION
AND A MARGINAL RISK OF SEVERE WEATHER OVER THE YUCATAN PENINSULA
TODAY. A DENSE PLUME OF SATURATED AIR IS EXPECTED TO REMAIN OVER
SOUTHERN MEXICO AND FROM SOUTHERN CENTRAL AMERICA TO THE
SOUTHEASTERN US, FUELING FAVORABLE DYNAMICS ALOFT. A LOW-LEVEL
TROUGH EXTENDING OVER THE SOUTHEASTERN GULF WILL SUPPORT STRONG
LOW-LEVEL MOISTURE CONVERGENCE AND HEAVY RAINFALL FROM THE EASTERN
YUCATAN PENINSULA TO WESTERN CUBA TODAY. LOCAL TERRAIN IN SOUTHERN
MEXICO WILL INTERACT WITH FAVORABLE CONDITIONS ALOFT TO TRIGGER
HEAVY THUNDERSTORMS OVER OAXACA TODAY. OVER THE NEXT FEW DAYS, THE
UPPER-LEVEL LOW WILL CONSTRAIN ITS CIRCULATION AROUND ITS CORE AND
WINDS WILL WEAKEN AS THE SYSTEM DRIFTS WESTWARD. IN THE
MID-TO-LOWER LEVELS, THE CYCLONIC CIRCULATION WILL ELONGATE AND
WARM ITS CORE OVER THE GULF OF MEXICO, CAUSING THE TROUGH
EXTENDING OVER THE REGION TO TRANSITION INTO A TROPICAL WAVE BY
THE END OF THE WEEK AS IT MOVES OVER THE WESTERN GULF. THIS SETUP
WILL FAVOR AN UNSTABLE ATMOSPHERE IN THE PRESENCE OF A PLUME OF
SATURATED AIR, SUSTAINING MODERATE TO SIGNIFICANT RAINFALL
ACCUMULATIONS ACROSS NORTHERN CENTRAL AMERICA TO THE EAST COAST OF
MEXICO BY SATURDAY. A MID-TO-LOW-LEVEL CYCLONIC CIRCULATION WILL
DEVELOP OFF SOUTHWESTERN MEXICO DUE TO THE INCREASE OF POSITIVE
POTENTIAL VORTICITY ASSOCIATED WITH THE MONSOON TROUGH AND
HORIZONTAL SHEAR OVER THE REGION. THESE CONDITIONS WILL SUPPORT
STRONG LOW-LEVEL MOISTURE CONVERGENCE AND SIGNIFICANT MID-LEVEL
POSITIVE VORTICITY TO TRIGGER HEAVY THUNDERSTORMS OVER THE SIERRA
MADRE DEL SUR OVER THE NEXT FEW DAYS.
OVER THE NEXT THREE DAYS, THE MONSOON TROUGH WILL REMAIN EXTENDED
ACROSS WESTERN CENTRAL AMERICA, FAVORING POSITIVE LOW-LEVEL
CYCLONIC ROTATION AND MOISTURE CONVERGENCE. UPPER-LEVEL DIVERGENCE
WILL SUPPORT UPWARD MOISTURE TRANSPORT FROM NICARAGUA TO PANAMA.
MODERATE TO HEAVY RAINFALL ACCUMULATION IS FORECAST OVER THE
REGION WITH MAXIMUM TOTALS IN THE 25-50 MM RANGE, WITH THE HIGHEST
PROBABILITIES OVER COSTA RICA AND PANAMA. LOW-LEVEL MOISTURE
ADVECTION FROM THE EASTERN PACIFIC INTERACTING WITH LOCAL
OROGRAPHY OVER NORTHWESTERN SOUTH AMERICA (SAM) WILL LEAD TO
LOW-LEVEL MOISTURE CONVERGENCE, TRIGGERING THUNDERSTORM
DEVELOPMENT OVER NORTHWESTERN COLOMBIA TODAY. UPPER-LEVEL
DIVERGENCE WILL SUPPORT UPWARD MOISTURE TRANSPORT FROM
NORTHWESTERN SAM TO THE CENTRAL AMAZON BASIN. A TROPICAL WAVE
EXTENDING OVER EASTERN VENEZUELA AND A SERIES OF LOW-LEVEL
SHORTWAVES WILL ENHANCE MOISTURE CONVERGENCE OVER THE ORINOQUIA,
NORTHWESTERN, AND WESTERN AMAZON BASINS, WHERE RAINFALL TOTALS OF
UP TO 20-35 MM ARE FORECAST TODAY. AS THE TROPICAL WAVE PROPAGATES
WESTWARD TOMORROW (FRIDAY), A REGION OF LOW-LEVEL MOISTURE
CONVERGENCE OVER ORINOQUIA WILL BECOME CONSTRAINED OVER COLOMBIA,
WHILE A SECOND REGION FOCUSES OVER THE WESTERN AND NORTHWESTERN
AMAZON BASIN. LOW-LEVEL MOISTURE DIVERGENCE WILL BUILD INTO THE
REGION OVER SUBSEQUENT DAYS, DRYING CONDITIONS OUT BY SATURDAY
ACROSS MUCH OF THE AREA. OVER THE NORTHWESTERN SAM COAST,
MID-LEVEL POSITIVE POTENTIAL VORTICITY ADVECTION FROM THE EAST
WILL INTERACT WITH PACIFIC LOW-LEVEL MOISTURE ADVECTION AND
TERRAIN-FORCED CONVECTION TO SUPPORT MODERATE TO HEAVY SHOWERS.
RAINFALL ACCUMULATION MAXIMA OF 25-50 MM ARE EXPECTED OVER THE
PACIFIC COAST OF COLOMBIA.
TROPICAL WAVES INITIALIZED AT 12 UTC:
TYP SOF INIT 02/00 02/12 03/00 03/12 04/00 04/12 05/00 05/12
TW 14N 32W 34W 37W 40W 44W 48W 52W 54W 56W
TW 18N 65W 67W 69W 71W 74W 77W 80W 82W 84W
SANCHEZ-PEREZ...(WPC)
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