000
AXPZ20 KNHC 281545
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SAT JUL 28 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1530 UTC.

...TROPICAL WAVES...
A TROPICAL WAVE ALONG 138W-139W S OF 18N CONTINUES TO MOVE W 
NEAR 13 KT. A WELL DEFINED MID LEVEL CYCLONIC CIRCULATION 
REMAINS EVIDENT IN SATELLITE IMAGERY AND TPW ANIMATIONS...WITH 
BEST MOISTURE CONVERGENCE LOCATE TO E OF AXIS. A WEAK AND 
FILLING SURFACE LOW WAS SUGGESTED BY AN EVENING WINDSAT 
PASS...AND COULD STILL REMAIN NEAR THE SURFACE NEAR 11.5N139W. 
SCATTERED MODERATE CONVECTION WAS OCCURRING ACROSS THE S 
SEMICIRCLE OF THE APPARENT LOW TO MID LEVEL CYCLONE...AND IN 
BANDS ON THE BACKSIDE OF THE WAVE...IN A N TO S ORIENTED 
CONVERGENCE BAND ALONG 136W.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
THE MONSOON TROUGH EXTENDS FROM LOW PRES 1009 MB ACROSS THE 
EXTREME SW CARIB NEAR 09.5N77.5W AND MEANDERS W TO 08N100W THEN 
TO 11N118W...THEN TRANSITIONS TO ITCZ...CONTINUING ON TO 
06.5N129W TO A TROPICAL WAVE ALONG 137W-138W BETWEEN 07N AND 
18N...WITH ITCZ CONTINUING ON W OF 140W. SCATTERED MODERATE TO 
STRONG CONVECTION NOTED FROM 04N TO 11N E OF 102W. SCATTERED 
MODERATE CONVECTION NOTED WITHIN 270 NM EITHER SIDE OF TROUGH 
FROM 109W TO 117W. SCATTERED MODERATE ISOLATED STRONG CONVECTION 
NOTED WITHIN 180 NM S OF ITCZ FROM 118W TO 130W. SCATTERED 
MODERATE TO STRONG CONVECTION NOTED WITHIN A 120 NM RADIUS OF 
18.5N106W.

...DISCUSSION...
TROUGH-RIDGE-TROUGH PATTERN PREVAIL IN THE MIDDLE TO UPPER 
LEVELS N OF 20N W OF 118W THIS MORNING. N OF 20N E OF 118W...A 
BLOCKING MIDDLE/UPPER LEVEL RIDGE PERSISTS OVER NW MEXICO AND 
THE DESERT SW OF THE U.S. A NARROW UPPER RIDGE EXTENDS SW TO 
17N122W TO 15N136W...WITH NE TO ELY UPPER FLOW GENERALLY 
PREVAILING S OF THIS RIDGE ACROSS THE DEEP TROPICS. A TUTT LOW 
OVER THE S CENTRAL GULF OF MEXICO EXTENDS WEAK INVERTED 
TROUGHING S-SW ACROSS SE MEXICO AND THE CHIVELAS PASS TO NEAR 
13N97W.  

A NARROW HIGH PRES RIDGE EXTENDS NEARLY W TO E ALONG 36N AND W 
OF 127W. THE SURFACE PRES GRADIENT BETWEEN THIS RIDGE AND LOWER 
PRES NEAR THE ITCZ IS COMBINING WITH THE TROPICAL WAVE ALONG 
137W-138W TO PRODUCE A BROAD AREA OF NE TO E WINDS 20-25 KT FROM 
11N TO 17N W OF 134W...WITH SEAS THERE RUNNING 8 TO 10 FT...AS 
VERIFIED BY AN OVERNIGHT ALTIMETER PASS. THE TROPICAL WAVE WILL 
CONTINUE TO MOVE W AND EXIT THE AREA IN THE NEXT 24-36 
HOURS...BUT THE GRADIENT WILL PERSIST LEAVING A SLIGHTLY SMALLER 
AREA OF 20 KT WINDS THROUGH EARLY MON. 

A LOW LEVEL WIND SURGE ASSOCIATED WITH THE REMNANTS OF AN OLD 
TROPICAL WAVE HAS MOVED ACROSS THE SW CARIBBEAN AND CENTRAL 
AMERICA DURING THE PAST 24-48 HOURS AND IS PRESENTING YIELDING 
GOOD MOISTURE CONVERGENCE ALONG THE MONSOON TROUGH E OF 94W AND 
VERY ACTIVE CONVECTION MENTIONED ABOVE. THIS HAS ALSO PRODUCED 
AN ELONGATED PLUME OF NE TO E WINDS TO 25 KT THROUGH AND 
DOWNWIND OF THE GULF OF PAPAGAYO TO 91W...AND WILL CONTINUE 
THROUGH ABOUT 36 HOURS...BEFORE A WEAK WAVE OR LOW BEGINS TO 
DEVELOP ALONG 93W...AND THE ELONGATED PLUME THEN EXPECTED TO 
SEPARATE INTO TWO SEGMENTS. ALSO...NORTHERLY WINDS TO 20 KT HAVE 
BEGUN TO SPILL FROM SE MEXICO THROUGH THE GULF OF TEHUANTEPEC 
AND WILL SPREAD DOWNWIND TOWARD THE SW IN A NARROW PLUME OVER 
THE NEXT TWO DAYS. 

$$
STRIPLING