Prognostic Meteorological Discussion
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000
FXSA20 KWBC 311738
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
137 PM EDT MON AUG 31 2015

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM AUG 31 AT 0000 UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS ARE IN GOOD AGREEMENT ON FORECAST EVOLUTION
THROUGH 84-96 HRS. CONFIDENCE STARTS DECREASING GRADUALLY
AFTERWARDS TO THE SOUGH OF 25S. THE MODELS ARE STRUGGLING ON THE
TIMING OF AN UPPER TROUGH TO CROSS CENTRAL CHILE INTO ARGENTINA
FROM THE EASTERN PACIFIC. THE GFS IS THE MOST AGGRESSIVE IN SPEED
AS IT CROSSES THE TROUGH DURING SATURDAY. THE OTHER MODELS ARE
FAVORING A WEAKENING SYSTEM APPROACHING THE ANDES DURING SUNDAY
INTO EARLY NEXT WEEK.

BROAD AND STRONG RIDGE PATTERN IS ESTABLISHING IN
CENTRAL/CENTRAL-WESTERN PORTIONS OF SOUTH AMERICA. THIS WILL LEAD
TO QUIET PATTERN THROUGH THE NEXT SEVERAL DAYS WITH ACTIVITY
CONSTRAINING TO THE NORTHWESTERN AMAZON BASIN AND EXTREME SOUTHERN
CHILE. ACROSS THE NORTHWESTERN AMAZON...THE SOUTHERN TAIL OF A
TROPICAL WAVE ASSOCIATED WITH FORMER TROPICAL STORM ERIKA IS
INTERACTING WITH A DEVELOPING TUTT OVER CENTRAL/WESTERN BRASIL.
THE TUTT IS FORECAST TO RETROGRESS TOWARDS THE EASTERN PACIFIC
THROUGH THE WEEK. BY MONDAY EVENING TUTT WILL CENTER OVER MATO
GROSSO-RONDONIA. BY TUESDAY EVENING IT WILL CENTER OVER ACRE. BY
WEDNESDAY EVENING OVER UCAYALI IN PERU...TO THEN BECOME ABSORBED
IN THE UPPER NORTHWESTERLIES ACROSS SOUTHERN PERU. ASIDE FROM
ENHANCED CONVECTIVE INSTABILITY...VENTILATION WILL BE ENHANCED IN
THE NORTHWESTERN PERIPHERY OF THE TUTT AS IT MOVES INTO AN UPPER
RIDGE CENTERING OFF THE COAST OF NORTHERN PERU. THIS
VENTILATION...IN COMBINATION WITH ENHANCED CONVECTIVE
INSTABILITY...WILL LEAD TO ACCUMULATIONS OF 20-40MM/DAY ACROSS
NORTHERN PERU/EASTERN ECUADOR/SOUTHERN COLOMBIA THROUGH EARLY
TUESDAY. EXPECTING MAXIMA OF 15-30MM/DAY ACROSS CENTRAL PERO AND
MOST OF AMAZONAS IN BRASIL. BY TUESDAY INTO EARLY WEDNESDAY FOCUS
OF ACTIVITY WILL CONCENTRATE ACROSS THE SAME REGION WITH MAXIMA OF
15-30MM/DAY FROM ACRE NORTH INTO SOUTHERN COLOMBIA/EASTERN ECUADOR
AND EASTERN PERU. AMOUNTS WILL DECREASE AFTER WITH MAXIMA OF
15-25MM/DAY DURING WEDNESDAY EVENING...TO DECREASE AFTERWARDS.
ENHANCED ACTIVITY ACROSS THE WESTERN AMAZON WILL ALSO SUSTAIN AN
INCREASE IN PRECIPITABLE WATER IN THE PERUVIAN/BOLIVIAN ANDES.
THIS WILL ACTIVATE DIURNAL CONVECTION TO PRODUCE DAILY MAXIMA IN
THE ORDER OF 00-05MM/DAY.

TO THE SOUTH...PRECIPITATION WILL CONSTRAIN TO EXTREME SOUTHERN
CHILE WHILE RIDGE PATTERN DOMINATES MOST OF THE CONTINENT.
EXPECTING PRECIPITATION ALONG WESTERN SLOPES OF THE MAGALLANES
REGION WITH AMOUNTS PEAKING DURING TUESDAY AND WEDNESDAY WHEN
EXPECTING MAXIMA OF 10-15MM/DAY.

COASTAL SAO PAULO/RIO DE JANEIRO. A COLD FRONT IS APPROACHING THE
REGION AND WILL EXTEND ADVANCE DURING MONDAY INTO TUESDAY EVENING.
BY TUESDAY EVENING IT WILL EXTEND ALONG NORTHERN RIO DE
JANEIRO-CENTRAL SAO PAULO-PARANA-SOUTHERN PARAGUAY WHERE IT IS TO
LINGER FOR A COUPLE OT DAYS TO THEN START RETROGRESSING. THIS WILL
INITIALLY STIMULATE ACTIVITY ALONG THE SERRA DO MAR FROM
PARANA/SAO PAULO INTO RIO DE JANEIRO TO PRODUCE SCATTERED MAXIMA
OF 05-10MM/DAY BY TUESDAY INTO EARLY WEDNESDAY. DURING
WEDNESDAY...A WEAK TROUGH CROSSING THE CENTRAL ARGENTINEAN ANDES
WILL STIMULATE CYCLOGENESIS ACROSS RIO GRANDE DO SUL. THIS WILL
ENHANCE ACTIVITY SLIGHTLY TO FAVOR THE DEVELOPMENT OF
THUNDERSTORMS WITH MAXIMA OF 15-25MM/DAY. AMOUNTS WILL DECREASE
ONCE AGAIN AFTERWARDS. AFOREMENTIONED FRONT WILL LINGER ALONG THE
COASTS OF ESPIRITO SANTO INTO THE LATE WORK WEEK. A SHEAR LINE
WILL ALSO DEVELOP TO EXTEND INTO ALAGOAS BY WEDNESDAY EVENING.
THIS WILL SUSTAIN SCATTERED TRADE WIND CONVECTION ALONG THE
EASTERN COAST OF BRASIL WITH ACCUMULATIONS GENERALLY IN THE
05-10MM/DAY RANGE. ISOLATED HIGHER AMOUNTS ARE EXPECTED IN
ASSOCIATION WITH THE SHEAR LINE AND FRONT.

ROMERO...DMC (CHILE)
FARINA...DMH (PARAGUAY)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)

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