Typhoon NANMADOL Prognosis

[Jeb]

WDPN31 PGTW 021500

MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC//

SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W WARNING NR 16//

RMKS/

1. FOR METEOROLOGISTS.

2. PROGNOSTIC REASONING FOR 021200Z5 DEC TO 071200Z0 DEC 2004.

A. TYPHOON (TY) 30W (NANMADOL), LOCATED APPROXIMATELY 100 NM

NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD

AT 17 KNOTS OVER THE PAST 06 HOURS AND IS ABOUT TO MAKE LANDFALL

SOUTH OF THE CITY OF CASIGURAN. THE WARNING POSITION IS BASED ON

021130Z7 ENHANCED INFRARED SATELLITE IMAGERY. THE WARNING

INTENSITY IS BASED ON SATELLITE CURRENT INTENSITY ESTIMATES OF

90, 115 AND 140 KNOTS. A RECENT 021200Z5 SYNOPTIC OBSERVATION

AT CASIGURAN REPORTS THAT THE WINDS HAVE SWITCHED FROM THE NORTH

TO THE NORTHEAST WITH SUSTAINED SPEEDS OF 58 KNOTS.

B. TY 30W IS FORECAST TO CONTINUE TO TRACK WEST-NORTHWESTWARD

INTO LUZON, PHILLIPINES ALONG THE SOUTHWESTERN PERIPHERY OF THE

SUBTROPICAL RIDGE ANCHORED TO THE NORTHEAST. TY 30W WILL SOON EXIT

LUZON TOWARDS A WEAKNESS IN THE SUBTROPICAL RIDGE CAUSING IT

TO SLOW DOWN IN THE SOUTH CHINA SEA. A MAJOR SHORTWAVE TROUGH (MSWT)

WILL EXIT ASIA AND LINK UP WITH TY 30W AT APPROXIMATELY THE 48 HR TAU.

TY 30W IS EXPECTED TO BEGIN TO INTERACT WITH A STRONG BAROCLINIC

BOUNDARY IN THE VICINITY OF TAIWAN AT THE 48 HR TAU AND BEGIN

TRANSITIONING TO AN EXTRATROPICAL LOW. TY 30W WILL BECOME EMBEDDED

IN THE MID-LATITUDE WESTERLY FLOW, ACCELRATE RAPIDLY TO THE NORTH-

EAST AND COMPLETE TRANSITION TO AN EXTRATROPICAL LOW BY THE 72 HOUR

TAU. THE AVAILABLE DYNAMIC AIDS CONSISTING OF NOGAPS, COAMPS, GFDN,

AFWA MM5, NCEP GFS, JGSM, JTYM, TCLAPS, UKMET, AND WBAR ARE IN FAIR

AGREEMENT ON TRACK BUT POOR AGREEMENT WITH SPEED. JGSM AND JTYM ARE

MARGINAL OUTLIERS TRACKING THE SYSTEM FURTHER EQUATORWARD. NCEP GFS

AND UKMET ARE MUCH FASTER DUE TO PROBABLE EXCESSIVE INTERACTION WITH

THE MID-LATITUDE FLOW; WBAR, TCLI, GFNI AND COWI ARE MUCH SLOWER.

THIS FORECAST IS BASED ON A CONSENSUS OF ALL AVAILABLE DYNAMIC AIDS

WITH HIGH UNCERTAINTY FOR THE SPEED OF ADVANCE OF TY 30W AFTER TAU 48.

C. THE INTENSITY OF STY 30W IS FORECAST TO CONTINUE TO DECREASE

AS IT INTERACTS WITH LAND AND ENCOUNTERS MODERATE VERTICAL SHEAR

IN THE SOUTH CHINA SEA. AFTER THE 48 HOUR TAU, TY 30W WILL EXPERIENCE

UNFAVORABLE VERTICAL SHEAR CONDITIONS AS IT ACCELERATES NORTHEASTWARDS

INTO THE MID-LATITUDE FLOW AND BECOMES AN EXTRATROPICAL LOW.

D. CURRENT WIND RADII ARE BASED ON A 021202Z8 QUIKSCAT PASS.

FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR A LARGE SIZED SYSTEM.

3. FORECAST TEAM: GRUBER/CHRISTIAN/LEWIN//