Tropical Storm CHAN-HOM Advisory Wed Jul 08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (CHAN-HOM) WARNING NR 35//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 09W (CHAN-HOM), LOCATED APPROXIMATELY 261 NM SOUTH-
SOUTHEAST OF KADENA AB, HAS TRACKED NORTHWESTWARD AT 12 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MSI DEPICTS THINNING DEEP
CONVECTION WITH A 28 NM DIAMETER EYE. THE CURRENT POSITION IS BASED
ON THE EYE FEATURE WITH HIGH CONFIDENCE. THE INITIAL INTENSITY
REMAINS AT 90 KNOTS BASED ON DVORAK CURRENT INTENSITY ESTIMATES FROM
PGTW. UPPER-LEVEL ANALYSIS INDICATES TY 09W IS LOCATED IN AN AREA OF
LOW TO MODERATE (10 TO 20) VWS BEING OFFSET BY THE EXCELLENT
EQUATORWARD OUTFLOW AS EVIDENT ON THE WATER VAPOR IMAGERY. THE
CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF AN EXTENSION
OF THE STR TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 09W IS FORECAST TO CONTINUE TRACKING NORTHWESTWARD UNDER
THE STEERING INFLUENCE OF THE STR THROUGH TAU 72. FAVORABLE
CONDITIONS WILL PERSIST, ALLOWING TY CHAN-HOM TO STEADILY INTENSIFY
LEADING TO A PEAK INTENSITY OF 115 KNOTS BY TAU 36. AFTERWARD, TY
CHAN-HOM IS EXPECTED TO BEGIN ITS WEAKENING TREND AS THE SYSTEM
INTERACTS WITH THE EASTERN COAST OF CHINA. DYNAMIC GUIDANCE IS IN
TIGHT AGREEMENT THROUGH THIS PERIOD, LENDING HIGH CONFIDENCE TO THIS
PORTION OF THE TRACK FORECAST.
   C. IN THE EXTENDED TAUS, AN APPROACHING MID-LATITUDE TROUGH WILL
PASS TO THE NORTH, CAUSING A BREAK IN THE STR AND ALLOWING TY 09W TO
TURN NORTHEASTWARD. UNFAVORABLE ENVIRONMENTAL CONDITIONS ALONG WITH
LAND INTERACTION WILL FURTHER DECAY THE SYSTEM. NUMERICAL MODEL
GUIDANCE SHOWS A LARGE SPREAD AND SIGNIFICANT DIFFERENCES IN THE
TRACK SPEEDS; THEREFORE, DUE TO SOME UNCERTAINTY IN TIMING AND SPEED
OF THE SYSTEM IN THE EXTENDED FORECAST TRACK, THE JTWC TRACK
FORECAST CONFIDENCE LEVEL REMAINS LOW.//
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