000
AXPZ20 KNHC 180958
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL                         
1005 UTC WED FEB 18 2015

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 
0900 UTC. 
  
...SPECIAL FEATURES...

GULF OF TEHUANTEPEC GALE WARNING...STRONG SURFACE HIGH PRESSURE 
IS BUILDING INTO SOUTHERN MEXICO BEHIND A COLD FRONT THAT IS 
MOVING ACROSS THE GULF OF MEXICO. THE TIGHT SURFACE PRESSURE  
GRADIENT ALONG WITH A PUSH OF DENSE DRY AND COOL AIR THROUGH THE 
CHIVELA PASS IN SOUTHERN MEXICO IS RESULTING IN GALE-FORCE 
WINDS IN THE GULF OF TEHUANTEPEC RIGHT NOW. 

OBSERVATIONS FROM SIX HOURS AGO OR SO ALONG THE COAST OF 
VERACRUZ IN THE SOUTHWESTERN GULF OF MEXICO WERE INDICATING 
STRONG PEAK WINDS. MINATITLAN (MMMT) ON THE NORTHERN END OF THE 
ISTHMUS OF TEHUANTEPEC WAS REPORTING GUSTS TO 30 KT...AN 
INDICATION OF THE GRADIENT FLOW ALREADY ENTERING INTO THE GAP. 
THIS WIND FLOW WILL MIX TO THE SURFACE MORE AND MORE FOR THE 
NEXT 24 TO 48 HOURS IN THE GULF OF TEHUANTEPEC.

THE SEA HEIGHTS WILL BUILD DOWNSTREAM OF THE GULF OF 
TEHUANTEPEC...REACHING AS HIGH AS 16 FEET BY LATE WEDNESDAY INTO 
EARLY THURSDAY. THE GALE-FORCE WINDS WILL PERSIST THROUGH LATE 
THURSDAY...FOR THE NEXT 48 HOURS...AND THEN DIMINISH AS THE HIGH 
PRESSURE THAT IS TO THE NORTH OF THE AREA WEAKENS AND SHIFTS 
EASTWARD.
                   
...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...

THE ITCZ EXTENDS FROM 03N91W TO 04N103W TO 03N112W TO 06N130W TO 
06N140W. CONVECTIVE PRECIPITATION...SCATTERED MODERATE TO 
ISOLATED STRONG WITHIN A 30 NM RADIUS OF 5N101W...AND FROM 06N 
TO 15N BETWEEN 116W AND 135W. 

...DISCUSSION... 

A MIDDLE LEVEL TO UPPER LEVEL TROUGH PASSES THROUGH 32N136W TO 
25N134W...TO A CYCLONIC CIRCULATION CENTER THAT IS BEING CUT OFF 
FROM THE REST OF THE FLOW NEAR 24N130W. THE TROUGH CONTINUES TO 
16N134W 09N132W AND TO 04N128W. THE CUT-OFF CYCLONIC CENTER IS 
THE SOUTHERN REMNANT OF AN UPPER LEVEL TROUGH THAT MOVED THROUGH 
THE REGION YESTERDAY...BUT THAT MOSTLY HAS MOVED TO THE 
NORTHEAST OF THE AREA. THE TROUGH WAS SUPPORTING A COLD FRONT 
THAT BECAME STATIONARY...AND NOW IS A SURFACE TROUGH THAT IS 
ALONG 30N136W TO 23N138W. CONVECTIVE PRECIPITATION...ISOLATED TO 
WIDELY SCATTERED MODERATE AND LOCALLY STRONG ELSEWHERE FROM 11N 
TO 30N BETWEEN 120W AND 140W. SHIP OBSERVATIONS AND 
SCATTEROMETER DATA WERE INDICATING MODEST WINDS NEAR THE FRONT 
12 HOURS AGO OR SO. A PAIR OF ALTIMETER SATELLITE PASSES FROM 
THAT TIME PERIOD NEAR THE FRONT CONFIRMED WAVE HEIGHTS OF 8 TO 
12 FEET. THIS SITUATION IS DUE TO LONG PERIOD SWELL FROM THE 
NORTHWEST. THE SWELL IS FORECAST TO DECAY TO 8 FEET AS IT 
PROPAGATES SOUTHEASTWARD AND SHRINKS IN AREAL EXTENT. THIS SWELL 
WILL MIX WITH SHORTER PERIOD TRADE WIND SWELL FROM 08N TO 14N 
BETWEEN 120W AND 127W THROUGH 48 HOURS. OTHER CONVECTIVE 
PRECIPITATION...SCATTERED MODERATE TO ISOLATED STRONG FROM 
06N TO 15N BETWEEN 116W AND 135W. 

A SURFACE TROUGH IS IN THE ITCZ ALONG 11N129W 8N131W 05N131W. 
NEARBY TRADE WIND FLOW IS BLOWING AT 15 TO 20 KNOTS. UPPER LEVEL 
FEATURES WILL WEAKEN GRADUALLY BUT REMAIN GENERALLY IN PLACE 
DURING THE NEXT 24 TO 48 HOURS. THIS WILL KEEP THE SURFACE 
TROUGH IN PLACE AS WELL. THE SUBTROPICAL RIDGE WILL STRENGTHEN 
BY THURSDAY MORNING...ALLOWING FOR A SLIGHTLY TIGHTER SURFACE 
PRESSURE GRADIENT BETWEEN THE TROUGH AND THE RIDGE. THE TRADE 
WIND FLOW WILL BE ENHANCED SOMEWHAT FROM 10N TO 20N BETWEEN 120W 
AND 130W. 

$$
MT