East Pacific Tropical Weather Discussion

000
AXPZ20 KNHC 150948
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SAT SEP 15 2012

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS 
BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND 
METEOROLOGICAL ANALYSIS.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0945 UTC.

...SPECIAL FEATURES...

TROPICAL STORM KRISTY CENTERED NEAR 21.8N 114.6W AT 0900 UTC 
MOVING NW OR 310 DEG AT 8 KT. MAXIMUM SUSTAINED WINDS ARE 40 KT 
WITH GUSTS TO 50 KT AND MINIMUM PRESSURE OF 1001 MB. THE SYSTEM 
APPEARS TO BE WEAKENING WITH ONLY SCATTERED MODERATE CONVECTION 
OBSERVED WITHIN 90 NM OVER THE E AND 30 NM OVER THE W 
SEMICIRCLES OF KRISTY. KRISTY IS FORECAST TO TRACK IN A GENERAL 
NW DIRECTION OVER COOLER SEA SURFACE TEMPERATURES AND IS 
EXPECTED TO WEAKEN TO A REMNANT LOW PRESSURE NEAR 25N118W ON 
SUN. SOUTHERLY SWELL FROM KRISTY IS MIXING WITH NW LONG PERIOD 
SWELL RESULTING IN COMBINED SEAS TO 8 FT REACHING THE PACIFIC 
COAST THE BAJA CALIFORNIA PENINSULA FROM 24N TO 26N TODAY...WITH 
THESE CONDITIONS SHIFTING N TO ALONG THE CENTRAL PORTION OF THE 
PENINSULA TONIGHT...THEN THE SEAS SHOULD SUBSIDE TO 3 TO 5 FT 
ALONG THE ENTIRE PACIFIC COAST OF THE PENINSULA LATE SUN. SEE 
THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS 
MIATCMEP1/WTPZ21 KNHC FOR MORE DETAILS.

TROPICAL LOW PRESSURE IS ANALYZED WITHIN THE MONSOON TROUGH NEAR 
14N122W AN ESTIMATED OF 1005 MB. SCATTERED MODERATE TO STRONG 
CONVECTION HAS BURST WITHIN 60 NM EITHER SIDE OF A LINE FROM  
11.5N124.5W TO 14N122W. THIS SYSTEM HAS THE POTENTIAL TO DEVELOP 
INTO A TROPICAL CYCLONE FORMATION AS IT TRACKS W TO NEAR 
14N124.5W TONIGHT...AND NEAR 16N127W SUN NIGHT. 

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...

THE MONSOON TROUGH AXIS EXTENDS W FROM THE NW COAST OF COLOMBIA 
AT 08N77W ACROSS WESTERN PANAMA AND SOUTHERN COSTA RICA TO 
09N85W...THEN TURNS SLIGHTLY SW TO 08N95W...SLIGHTLY NW TO NEAR 
10N115W WHERE IT LOSES IDENTITY. THE MONSOON TROUGH RESUMES SW 
OF TROPICAL CYCLONE KRISTY NEAR 17N116W...AND CONTINUES SW 
THROUGH EMBEDDED LOW PRESSURE CENTERS AT 14N122W AND 12N134W... 
THEN CONTINUES SW TO BEYOND 11N140W. SCATTERED MODERATE ISOLATED 
STRONG CONVECTION IS OBSERVED WITHIN 180 NM EITHER SIDE OF A 
LINE FROM 09N92W TO 14N103W...AND A LINE FROM 06N105W TO 
09N118W. ISOLATED MODERATE TO STRONG CONVECTION IS NOTED WITHIN 
120 NM EITHER SIDE OF A LINE FROM 09N124W TO 14N134W.

...DISCUSSION...

A LONGWAVE UPPER RIDGE DOMINATES THE EASTERN N PACIFIC STEMMING 
FROM AN UPPER ANTICYCLONE CENTERED AT 25N127W AND RIDGING NE TO 
BEYOND 32N121W. AN UPPER RIDGE ALSO EXTENDS SW TO A CREST AT 
12N145W. AN UPPER SHORTWAVE TROUGH HAS MOVED OVER THE NW PORTION
WITH AN EMBEDDED UPPER CYCLONE AT 29N140W...SETTING UP A 
SOUTHERLY JET AT 60 TO 90 KT OVER THE NW PORTION WITHIN 180 NM 
OF LINE FROM 23N140W TO 30N135W. WEAK UPPER DIFFLUENCE OVER THE 
DEEP TROPICS IS ENHANCING CONVECTION ALONG THE MONSOON TROUGH 
BETWEEN 120W AND 140W...INCLUDING THE CONVECTION ACCOMPANYING 
THE TROPICAL LOW AT 14N122W. SOME OF THE DEBRIS MOISTURE IS 
ADVECTED SW TO ALONG 04N BETWEEN 120W AND 130W...AND SOME OF THE 
DEBRIS MOISTURE IS ALSO ADVECTED N ACROSS THE UPPER RIDGE AXIS 
BETWEEN 132W AND 137W...THEN THE NARROW PLUME OF MOISTURE TURNS 
NE TO NEAR 26N129W WHERE IT EVAPORATES IN THE VERY DRY THAT IS 
INDICATED OVER THE DISCUSSION AREA N OF 17N BETWEEN 117W AND 
140W. THE UPPER ANTICYCLONE IS EXPECTED TO SHIFT NE TO NEAR 
28N120W LATE SUN AS THE UPPER CYCLONE ALSO SHIFTS N TO NEAR 
35N140W DRAGGING AN UPPER TROUGH OVER THE EXTREME NW PORTION OF 
THE DISCUSSION AREA.

IMMEDIATELY TO THE E OF THE LARGE UPPER RIDGE IS A DEEP LAYERED 
CYCLONE OVER NEW MEXICO WITH AN UPPER TROUGH EXTENDING S ACROSS 
THE CENTRAL BAJA PENINSULA INTO AN UPPER CYCLONE NEAR TROPICAL 
CYCLONE KRISTY...WITH THE UPPER TROUGH CONTINUING S TO NEAR 
08N119W. UPPER DIFFLUENCE ALONG AND E OF THIS TROUGH HAS 
ENHANCED CONVECTION OVER INTERIOR NORTHWESTERN OLD MEXICO... 
OVER TROPICAL CYCLONE KRISTY...AND ALSO SEEMS TO A CONTRIBUTOR 
TO THE TROPICAL CONVECTION NEAR 09N114W. THE RESULTANT DEBRIS 
MOISTURE TO THE N OF 25N IS SPREADING NE OVER THE NORTHWESTERN 
MEXICO AND THEN ACROSS EASTERN TEXAS AND EVENTUALLY TURNING E 
ACROSS THE APPALACHIANS. THE DENSE MOISTURE TO THE S OF 25N IS 
CONCENTRATES INTO A 500 NM WIDE PLUME WITH AXIS FROM 25N105W TO 
04N118W. 

A BROAD INVERTED UPPER TROUGH IS NOTED OVER THE DEEP TROPICAL 
PACIFIC TO THE S OF 16N BETWEEN 98W AND 108W...AND IS SHIFTING 
WESTWARD WITH TIME...AND WILL LIKELY MERGE WITH HE SOUTHERN 
PORTION OF THE UPPER TROUGH CURRENTLY DESCRIBED ALONG 120W ON 
SUN. AN UPPER ANTICYCLONE IS OVER THE NW CARIBBEAN AT 17N84W 
WITH ITS ENVELOPE OF UPPER ANTICYCLONIC FLOW COVERING THE 
DISCUSSION AREA E OF 98W. THESE FEATURES COMBINE TO SET UP AN 
AREA OF UPPER DIFFLUENCE OVER CENTRAL AMERICA AND THE TROPICAL 
PACIFIC TO THE E OF 105W. UPPER DEBRIS MOISTURE IS NOTED TO THE 
N OF 05N E OF 105W. 

ELSEWHERE AT THE SURFACE...A BROAD RIDGE COVERS THE AREA N OF 
15N W OF 122W. A SURFACE RIDGE HAS BECOME ORIENTATED FROM NNW TO 
SSE OVER THE EASTERN PORTION OF OLD MEXICO...AND IS PRODUCING 
NORTHERLY SURGES AT 20 TO 25 KT INTO...AND JUST DOWNSTREAM...
OF THE GULF OF TEHUANTEPEC WITH LITTLE CHANGE EXPECTED THROUGH 
TONIGHT...THEN THESE WINDS SHOULD DIMINISH. NE TO E WINDS ARE 
EXPECTED TO PULSE AT 15 TO 20 KT THROUGH THE GULF OF PAPAGAYO 
WITH MAX SEAS OF 7 FT JUST DOWNSTREAM OF THE GULF THROUGH LATE 
TONIGHT. THE STRONGEST GAP WINDS ARE EXPECTED TO OCCUR DURING 
THE LATE NIGHT HOURS AND CONTINUE THROUGH A FEW HOURS AFTER 
SUNRISE.  

$$
NELSON