000
AXPZ20 KNHC 150343
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC THU JAN 15 2009

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN
FROM THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0315 UTC.

...ITCZ...

ITCZ IS CENTERED ALONG 6N78W 7N87W 5N100W 6N110W 7N121W 8N131W
6N140W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION EXISTS
FROM 9N-15N BETWEEN 125W-134W. SCATTERED MODERATE CONVECTION IS 
WITHIN 180 NM S OF THE AXIS BETWEEN 82W-87W.

...DISCUSSION...

THE REGION REMAINS IN BETWEEN TWO RATHER LARGE SCALE FEATURES.
THE FIRST IS THE TAIL END OF BROAD UPPER LEVEL TROUGHING 
CENTERED OVER MID-WEST REGION OF THE UNITED STATES WHICH REACHES 
INTO THE FAR EASTERN SECTION OF THE AREA TO N OF ABOUT 22N AND E 
OF 118W. W OF THE TROUGH...THE AREA IS UNDER MID AND UPPER LEVEL 
RIDGING PRESENT N OF 22N WITH AN ANTICYCLONIC CENTER OF 1023 MB
N OF THE AREA NEAR 35N131W. THE SECOND FEATURE CONTINUES TO BE
A RATHER EXTENSIVE LATITUDINAL DEEP LAYER TROUGH IS JUST W OF
THE REGION N OF 26N...WHILE IT STRETCHES ALONG 137W/138W FROM
7N TO 26N. A MID/UPPER LEVEL LOW MOVING E IS ALONG THE TROUGH 
AXIS NEAR 16.5N137W. THE ASSOCIATED SURFACE COLD FRONT IS NEARING
THE NW PORTION OF THE AREA...AND IS PRECEDED BY INCREASING SLY
WINDS AS NOTED IN A FEW 20 KT WIND OBSERVATIONS FROM SHIPS OVER
THOSE WATERS.

DATA INFERRED FROM SATELLITE-DERIVED WINDS SHOWS QUITE A LARGE
AREA OF UPPER LEVEL DIFFLUENCE ENHANCING SCATTERED MODERATE TO
ISOLATED STRONG CONVECTIVE CLUSTERS TO THE E OF THE BASE OF
THE TROUGH ALONG AND N OF THE ITCZ AXIS FROM 8N TO 15N BETWEEN
125W AND 136W. EXPECT THIS ACTIVITY TO CONTINUE OVER THE NEXT
FEW DAYS AS THE TROUGH GRADUALLY TRANSLATES EASTWARD. MODERATE 
TO STRONG UPPER LEVEL WINDS ARE ALONG AND W OF THE TROUGH AXIS
N OF 27N. THESE WINDS CONTINUE TO TRANSPORT UPPER LEVEL MOISTURE
IN THE FORM OF HIGH LEVEL CLOUDS N TO WELL N OF THE REGION. 

THE SURFACE COLD FRONT IS FORECAST TO SLOW ITS FORWARD MOTION AND
WEAKEN JUST NW OF THE AREA OVER THE THE NEXT 2-3 DAYS AS ITS 
DRIVING UPPER SUPPORT AND RELATED ENERGY PULLS FURTHER AWAY FROM 
THE AREA TOWARDS THE GENERAL VICINITY OF ALASKA AS GLOBAL MODELS 
ARE IN PRETTY CLOSE AGREEMENT WITH RESPECT TO THIS SCENARIO. 
HOWEVER...THE MAIN ISSUE WITH THIS FRONT AND THE VERY 
PROGRESSIVE UPPER LATITUDE FRONTAL SYSTEMS THAT FOLLOW BEHIND IT 
WILL BE LONG PERIOD NW SWELLS GENERATED BY ATTENDANT DEEP LOW 
PRES SYSTEMS THAT WILL ALSO PASS WELL TO THE N OF 30N OVER THE 
NEXT FEW DAYS. WAVEWATCH MODEL GUIDANCE IS VERY CONSISTENT IN 
SHOWING SIGNIFICANT WAVE HEIGHTS OF 13-15 FT ENTERING THE FAR NW 
CORNER BY LATE THU NIGHT...AND UP TO POSSIBLY 16 OR 17 FT BY FRI 
NIGHT WITH SEAS ELSEWHERE RANGING 9-15 FT W OF 130W. WILL HAVE 
TO MONITOR THIS UPCOMING SWELL EVENT CLOSELY WITH RESPECT TO 
PROJECTED FORECAST HEIGHTS AND AREAL COVERAGE AS PORTRAYED IN 
FUTURE MODEL GUIDANCE.

ELSEWHERE...A WEAK UPPER LEVEL CYCLONIC CIRCULATION MOVING 
WNW IS EMBEDDED IN THE AREA OF MID/UPPER LEVEL RIDGING NEAR 
26N129W WITH A TROUGH STRETCHING SEWD THROUGH 21N119W TO 17N113W 
TO NEAR 8N105W. MODERATE TO STRONG SW FLOW E OF THE UPPER TROUGH 
BECOMES CONFLUENT ALONG 22N E OF 118W OR ALONG THE BASE OF THE 
BROAD UPPER LEVEL TROUGH OVER THE EASTERN PART OF THE AREA. A 
JET STREAM BRANCH WITH MAXIMUM WINDS OF UP TO 75 KT ROUNDS THE 
BASE OF THE THIS TROUGH. POSSIBLE HIGH LEVEL TURBULENCE IN 
TRANSVERSE BANDING OF CIRRUS CLOUDS IS NOTED FROM 10N TO 20N E 
OF THE 117W. THE CONFLUENT FLOW ASSOCIATED WITH THE BROAD UPPER 
LEVEL TROUGH IS RESULTING IN MODERATE TO STRONG SUBSIDENCE 
INDUCING DRY STABLE AIR OVER MUCH OF THE AREA N OF 22N E OF THE
DEEP LAYER TROUGH DESCRIBED IN FIRST PARAGRAPH. BROAD UPPER 
LEVEL ANTICYCLONIC FLOW COVERS THE AREA S OF 20N AND TO THE W 
OF THE TROUGH ALONG 21N119W TO 17N113W TO 8N105W.

AT THE SURFACE...HIGH PRES RIDGING SWD OVER THE WESTERN GULF 
OF MEXICO AND MEXICO MAINTAINS A TIGHT PRES GRADIENT ALONG THE 
MEXICAN COAST USHERING GALE FORCE WINDS IN THE RANGE OF 
30-40 KT INTO THE GULF OF TEHUANTEPEC EARLY THIS EVENING.
THESE WINDS HAVE SINCE DIMINISHED SLIGHTLY DURING THE COURSE
OF THE EARLY EVENING...AND MAY DECREASE SLIGHTLY DURING THE
NEXT 12-18 HOURS BEFORE INCREASING AGAIN AS INDICATED BY THE 
LATEST 10M AND 30M MODEL WIND GUIDANCE. MODEL GUIDANCE SUGGESTS
THAT THESE WINDS MAY POSSIBLY REACH STORM FORCE AGAIN IN ABOUT
42-48 HOURS...BUT THIS SCENARIO WILL BE HIGHLY DEPENDENT ON
WHETHER GULF SSTS WILL BE WARM ENOUGH FOR DOWNWARD MOMENTUM OF
COLD AIR OVER TO ALLOW FOR SUFFICIENT MIXING OVER THESE WATERS
FOR STORM FORCE WINDS TO DEVELOP AT THAT TIME. WILL HAVE TO 
CLOSELY WATCH FOR CHANGES IN SSTS AS THEY BECOME AVAILABLE AS 
WELL AS STRENGTH OF HIGH PRES THAT DEVELOPS OVER NORTHERN MEXICO 
LATER IN THE WEEK.
 
NE WINDS OF 20-25 KT THROUGH THE GULF OF PAPAGAYO ARE EXPECTED
TO CHANGE LITTLE OVER THE NEXT 24 HOURS THEN INCREASE TO 30 KT 
IN 36 HOURS AS STRONG HIGH PRES RIDGING PRESSES SWD OVER CENTRAL 
AMERICA. THESE WINDS MAY DECREASE SLIGHTLY IN ABOUT 48 HOURS.
ELSEWHERE HIGH PRES COVERS THE AREA N OF ABOUT 16N W OF 110W.

$$
AGUIRRE