000
AXPZ20 KNHC 171602
TWDEP 

TROPICAL WEATHER DISCUSSION  
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC WED AUG 17 2011

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 
1500 UTC.

...SPECIAL FEATURES...
TROPICAL STORM FERNANDA AT 11.8N 137.8W 1001 MB AT 1500 UTC AUG 
17 MOVING W OR 275 DEG AT 8 KT. MAXIMUM SUSTAINED WIND 45 GUSTS 
55 KT. SCATTERED MODERATE CONVECTION WITHIN 120 NM SE 
SEMICIRCLE. FERNANDA EXPECTED TO MOVE W AND INTENSIFY SLIGHTLY 
OVER THE NEXT 24 HOURS...AND AND MOVE W OF THE DISCUSSION AREA 
THU. REFER TO FORECAST ADVISORIES ISSUED UNDER WMO HEADER WTPZ21 
KNHC AND AWIPS HEADER MIATCMEP1 FOR FURTHER DETAILS.

TROPICAL STORM GREG AT 16.7N 104.2W 1004 MB AT 1500 UTC AUG 17 
MOVING W-NW OR 300 DEG AT 18 KT. MAXIMUM SUSTAINED WIND 45 KT 
GUSTS 55 KT. NUMEROUS STRONG CONVECTION FROM 15N TO 18N BETWEEN 
104W AND 106W. TROPICAL STORM GREG EXPECTED TO INTENSIFY OVER 
WARM WATERS S OF MEXICO AND BECOME A HURRICANE WITHIN 24 HOURS. 
REFER TO FORECAST ADVISORIES ISSUED UNDER WMO HEADER WTPZ22 KNHC 
AND AWIPS HEADER MIATCMEP2 FOR FURTHER DETAILS.

...ITCZ/MONSOON TROUGH...
MONSOON TROUGH FROM 08N786W TO 09N85W TO 11N94W...THEN RESUMES 
FROM 15N110W TO LOW PRES 14N114W TO 11N123W TO 13N130W. 
SCATTERED MODERATE ISOLATED STRONG CONVECTION WITHIN 150 NM S OF 
AXIS FROM 116W TO 129W.

...DISCUSSION...
MODERATE EAST FLOW DOMINATES THE MID AND UPPER LEVELS OF THE 
ATMOSPHERE MAINLY E OF 120W...TO THE SOUTH OF A LARGE DEEP LAYER 
RIDGE CENTERED OVER THE SOUTH CENTRAL UNITED STATES AND NORTHERN 
MEXICO. THIS IS PROVIDING THE MAIN STEERING FLOW FOR T.S. GREG 
AS WELL AS SOME EASTERLY SHEAR ON THE STORM. GREG WILL 
EXPERIENCE DECREASING SHEAR AS IT MOVES RAPIDLY 
WESTWARD...TOWARD THE WESTERN EDGE OF THE RIDGE. A 1007 MB LOW 
IS NOTED TO THE WEST OF GREG NEAR 14N114W WITH WINDS  TO 20 KT 
OUT AS FAR AS 360 NM FROM THE CENTER. THIS SLOW WILL MOVE W 
AHEAD OF GREG THROUGH 24 HOURS ALONG 14N...THEN DISSIPATE 
THROUGH 48 HOURS.

SOUTH OF GREG...A MAINLY MID LEVEL DISTURBANCE IS NOTED EVIDENT 
IN SATELLITE IMAGERY OFF COSTA RICA ALONG 90W S OF 
13N...INTERACTING WITH THE MONSOON TROUGH. CONVECTION REMAINS 
FAIRLY LIMITED WITH THIS SYSTEM AND ALTHOUGH GFS AND ECMWF SHOW 
A WEAK CIRCULATION FORMING BY 24 HOURS AND DRIFTING W ALONG 
12N...CONVECTION AND WINDS WILL REMAIN LIMITED.

MODERATE CONVECTION IS NOTED ALONG THE MONSOON TROUGH BETWEEN 
115W AND 130W...DUE TO CONVERGENCE OF MODERATE SW FLOW.

SHIP DATA AND AN ASCAT PASS FROM 1640 UTC SHOWED WINDS TO 20 KT 
AS FAR AS 300 NM N OF THE CENTER...BETWEEN THE TROPICAL STORM 
AND HIGH PRES N OF THE AREA. DEEP LAYER DRY AIR W OF 120W AT THE 
BASE OF AN UPPER TROUGH ALONG 135W N OF 23N IS NOT ONLY 
SUPPRESSING CONVECTION RELATED TO T.S. FERNANDA...BUT IS ALSO 
LIMITING IN LARGE SCALE CONVECTION THROUGHOUT THE AREA W OF 120W.

MEANWHILE S SWELL TO 8 FT WITH PERIODS TO 14 SECONDS IS PUSHING 
ACROSS THE EQUATOR AS FAR N AS 14N BETWEEN 100W AND 114W. 

$$
CHRISTENSEN