000
AXPZ20 KNHC 182138
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC THU AUG 18 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2100 UTC.

...SPECIAL FEATURES...
HURRICANE GREG IS CENTERED NEAR 18.8N 112.6W AT 18/2100 UTC 
MOVING WEST NORTHWEST OR 285 DEGREES AT 12 KT. A TURN TOWARD THE 
WEST WITH A DECREASE IN FORWARD SPEED IS FORECAST DURING THE 
NEXT COUPLE OF DAYS. MAXIMUM SUSTAINED WIND SPEED IS 75 GUSTS TO 
90 KT. GREG IS A CATEGORY ONE HURRICANE ON THE SAFFIR-SIMPSON 
HURRICANE WIND SCALE. THE CENTER OF GREG IS MOVING OVER COOLER 
WATERS AND WEAKENING IS FORECAST DURING THE NEXT COUPLE OF DAYS. 
ESTIMATED MINIMUM CENTRAL PRESSURE IS 980 MB. NUMEROUS STRONG 
CONVECTION IS NOTED WITHIN 90 NM N SEMICIRCLE AND 180 NM S 
SEMICIRCLE. REFER TO FORECAST ADVISORIES ISSUED UNDER WMO HEADER 
WTPZ22 KNHC AND AWIPS HEADER MIATCMEP2 FOR FURTHER DETAILS.

...ITCZ/MONSOON TROUGH...
MONSOON TROUGH ANALYZED FROM 10N85W TO 10N100W...THEN RESUMES 
FROM 16N116W TO 13N132W. SCATTERED MODERATE TO ISOLATED STRONG 
WITHIN 120 NM N OF AXIS FROM 117W TO 127W. ISOLATED TO SCATTERED 
MODERATE FROM 05N TO 08N BETWEEN 80W AND 89W AND FROM 10N TO 13N 
BETWEEN 96W AND 104W.

...DISCUSSION...
AN UPPER LEVEL TROUGH IS CLIPPING THE FAR NW PORTION OF THE 
DISCUSSION AREA. AN ANTICYCLONIC CIRCULATION CENTERED OVER 
WESTERN TEXAS EXTENDS A RIDGE OVER THE SW UNITED STATES AND 
NORTHWESTERN MEXICO. GREG IS MOVING AROUND THE SOUTHERN 
PERIPHERY OF THIS RIDGE. A WEAK UPPER LEVEL INVERTED TROUGH 
EXTENDING FROM NORTHERN BAJA CALIFORNIA TO A CYCLONIC 
CIRCULATION NEAR 24N116W SEPARATES THE ABOVE MENTIONED 
ANTICYCLONE FROM ANOTHER ANTICYCLONIC CIRCULATION LOCATED NEAR 
28N121W. NE TO E UPPER LEVEL FLOW DOMINATES THE DEEP TROPICS.

A 1029 MB HIGH PRES SITUATED N OF AREA NEAR 42N135W EXTENDS A 
RIDGE OVER THE FORECAST WATERS MAINLY N OF 20N W OF 115W. THE 
MOST RECENT WINDSAT PASS SHOWS THAT FRESH TO STRONG WINDS 
ASSOCIATED WITH T.S. FERNANDA ARE STILL AFFECTING THE FORECAST 
WATERS FROM 10N TO 18N W OF 137W.  

THE 1524 UTC PROVIDED OBSERVATIONS OF NLY WINDS IN THE 15 TO 20 
KT RANGE ACROSS THE GULF OF TEHUANTEPEC. HOWEVER...IXTEPEC IN 
THE STATE OF OAXACA MEXICO IS REPORTING SUSTAINED WINDS OF 25 KT 
SINCE 1800 UTC.

FRESH TO STRONG MONSOONAL FLOW IS NOTED SW OF GREG COVERING THE 
AREA FROM 08N TO 13N BETWEEN 114W AND 122W. AN EARLIER WINDSAT 
PASS AND THE 1706 ASCAT PASS CONFIRMED THESE WIND SPEEDS. THE 
SAME ASCAT PASS SHOWED NE WINDS OF 20 TO 25 KT WITHIN ABOUT 150 
NM N OF THE MONSOON TROUGH BETWEEN 118W AND 121W. A WEAK LOW 
PRES WAS ANALYZED IN THIS AREA ABOUT 24 HOURS AGO.

ADDITIONAL PULSES OF CROSS EQUATORIAL SWLY SWELL WILL PROPAGATE 
ACROSS THE SOUTH WATERS E OF 110W DURING THE UPCOMING WEEKEND 
REACHING THE MEXICAN COAST EARLY ON SUN. 

$$
GR