746
FXSA20 KWBC 141948
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 PM EST TUE JAN 14 2025
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
SOUTH AMERICAN FORECAST BULLETIN FOR 14 JAN 2025 AT 1945 UTC:
OVER THE NEXT 3 DAYS...BRASIL IS EXPECTED TO RECEIVE SIGNIFICANT
RAIN...ESPECIALLY ACROSS THE EASTERN HALF. TODAY IS EXPECTED TO BE
THE RAINIEST DAY ACROSS THE EASTERN HALF OF BRASIL...FOLLOWED BY
WEDNESDAY INTO THURSDAY...THEN THURSDAY INTO FRIDAY WOULD BE EVEN
DRIER. THAT BEING SAID...THERE IS A SMALL AREA OF SOUTH CENTRAL
BRASIL THAT COULD OBSERVE AS MUCH AS 40-80MM. THE PRESENCE OF THE
ABOVE NORMAL MOISTURE OVER EASTERN BRASIL...COMBINED WITH THE NET
AND THE SACZ...WILL CONTRIBUTE TO THE EXPECTED ACTIVE WEATHER OVER
THE AREA TODAY AND WEDNESDAY. BY THURSDAY THOUGH...THE SACZ IS
EXPECTED TO HAVE DISSIPATED AND DRIER AIR WILL START TO MOVE INTO
EASTERN BRASIL...THEREFORE THE SHOWER ACTIVITY OVER EASTERN BRASIL
IS EXPECTED TO DIMINISH. HOWEVER...IN TERMS OF RAINFALL
TOTALS...MANY SECTORS OF EASTERN BRASIL ARE FORECAST RAINFALL
TOTALS MAXING OUT NEAR 35-80MM TODAY...BUT THERE IS A SMALL SECTOR
OF NORTHEASTERN BRASIL...NEAR THE COAST OF MARANHAO...PIAUI AND
CEARA...THAT COULD OBSERVE AS MUCH AS 75-125MM. IT PAYS TO KNOW
THAT THE GFS MODEL IS EVEN MORE AGGRESSIVE WITH THE FORECAST
RAINFALL AMOUNTS...BUT THE ECMWF HAS A LOWER SOLUTION...AND WE
WENT CLOSER TO THE ECMWF BASED ON RECENT OBSERVATIONS AND RECENT
MODEL PERFORMANCE. FOR WEDNESDAY INTO THURSDAY...PORTIONS OF
EASTERN BRASIL ARE FORECAST 25-50MM OF RAIN ALONG THE DISSIPATING
SACZ AND A SURFACE TROF...THOUGH FURTHER NORTH OVER BAHIA INTO
CEARA COULD OBSERVE 35-70MM...WHILE A SMALL SECTION OF MARANHAO IS
FORECAST ISOLATED AMOUNTS OF 40-80MM NEAR THE ITCZ. FURTHER SOUTH
AND WEST OF THE MENTIONED AREAS...THE RAINFALL FORECAST WOULD BE
AROUND 05-15MM WITH ISOLATED AMOUNTS SOMEWHERE BETWEEN 20-45MM.
THEN ON THURSDAY INTO FRIDAY...MOST OF BRASIL IS FORECAST
RELATIVELY MODEST AMOUNTS OF RAIN...WITH THE EXCEPTION OF THE
AFOREMENTIONED AREA IN SOUTH CENTRAL BRASIL THAT COULD OBSERVE
NEAR 40-80MM...MOST AREAS ARE FORECAST AROUND 05-15MM WITH
ISOLATED AMOUNTS UP TO 35MM. THAT BEING SAID...THERE IS A MARGINAL
RISK OF SEVERE WEATHER NEAR SAO PAULO.
THE MOUNTAINOUS REGION FROM PERU INTO BOLIVIA AND CHILE WILL HAVE
SHOWERS AND THUNDERSTORMS EACH DAY BUT THE RAINFALL TOTALS WILL BE
GENERALLY UP TO 25MM. THAT SAID...THE MODEL GUIDANCE IS SUGGESTING
AN AREA OF SOUTHERN PERU THAT COULD OBSERVE AS MUCH AS 30-60MM ON
THURSDAY INTO FRIDAY. SOUTHERN CHILE WILL ALSO OBSERVE SHOWER
ACTIVITY EACH DAY WITH THE RAINFALL TOTALS GENERALLY PEAKING AT
AROUND 15-25MM WITH MOUNTAIN SNOW EXPECTED. HOWEVER...A PATCH OF
MOISTURE IS FORECAST TO MOVE INTO SOUTHERN...OR AUSTRAL...CHILE
LATE THURSDAY INTO EARLY FRIDAY...CAUSING THE PRECIPITATION
AMOUNTS TO BE UP TO 35MM...WITH SOME MOUNTAIN SNOW.
IN THE UPPER LEVELS...THE BOLIVIAN HIGH CONTINUES TO WEAKEN...AND
ANOTHER HIGH PRESSURE IS STILL EXPECTED TO DEVELOP NEAR MINAS
GERAIS BY THURSDAY MORNING. A LOW PRESSURE WILL APPROACH THE
NORTHEASTERN COAST OF BRASIL ON WEDNESDAY. A LOW PRESSURE IN THE
WESTERN ATLANTIC...AS WELL AS A WEAK LOW PRESSURE OVER NORTHERN
ARGENTINA...ARE CAUSING RELATIVELY STRONG WINDS ALOFT OVER
SOUTHERN BRASIL INTO SOUTHERN PARAGUAY...WITH MAX SPEEDS NEAR 70
KNOTS. WESTERLY WINDS ARE FORECAST OVER SOUTHERN SOUTH
AMERICA...AS AN UPPER TROUGH MOVES THROUGH. THESE STRONG WINDS ARE
STILL FORECAST TO PEAK AT AROUND 135 KT ON WEDNESDAY.
IN THE MID LEVELS...THERE IS A SHORTWAVE TROUGH THAT HAS MOVED
OFFSHORE SOUTH AMERICA TODAY...BUT ANOTHER MID LEVEL TROUGH WILL
BE MOVING INTO SOUTHERN SOUTH AMERICA ON WEDNESDAY...THEN
ANOTHER...BUT RELATIVELY WEAK TROUGH...WILL MOVE IN LATE ON
THURSDAY. LIGHT MID-LEVEL WINDS ARE EXPECTED OVER MOST OF CENTRAL
TO NORTHERN SOUTH AMERICA...WITH A HIGH PRESSURE OVER PARA AND A
LOW PRESSURE OVER NORTHERN TO NORTHEASTERN ARGENTINA INTO SOUTHERN
PARAGUAY. THE MODEL GUIDANCE DOES INDICATE SOME AREAS OF HIGHER
VORTICITY OVER TROPICAL SOUTH AMERICA...WHICH WILL CONTRIBUTE TO
THE SHOWER AND THUNDERSTORM DEVELOPMENT EXPECTED.
IN THE LOW LEVELS...THE WINDS WILL BE FROM THE NORTH TO NORTHWEST
OVER NORTHERN SOUTH AMERICA...WHICH IS CONTRIBUTING TO THE
SUSTAINED SACZ EXTENDING FROM BAHIA TO THE MATO GROSSO AND BOLIVIA
BORDER. THAT SAID...THE LOW LEVEL WIND CONVERGENCE STARTS TO
BECOME WEAKER INTO WEDNESDAY...AND THUS WE HAVE A DISSIPATING SACZ
FOR WEDNESDAY INTO THURSDAY...THEN ONLY A TROUGH IN THE AREA FOR
THURSDAY AS A LOW-LEVEL LOW PRESSURE WILL THEN APPEAR TO BE
DEVELOPING OVER THE AREA. STRONG 850 HPA WINDS WILL MOVE INTO
SOUTH CENTRAL CHILE LATE TONIGHT INTO WEDNESDAY...BUT EVEN
STRONGER WINDS WILL MOVE INTO AUSTRAL CHILE AND ARGENTINA.
ALAMO...(WPC)
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