Tropical Storm ONE Advisory Tue Jul 21

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 01C (HALOLA) WARNING NR 46//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
  TYPHOON (TY) 01C (HALOLA), LOCATED APPROXIMATELY 159 NM SOUTHEAST
OF IWO TO, JAPAN, HAS TRACKED WESTWARD AT 11 KNOTS OVER THE PAST SIX
HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT SYSTEM WITH CURVED BANDING WRAPPED TIGHTER INTO A SYMMETRIC
5-NM EYE. THE INITIAL POSITION IS BASED ON THE EYE IN THE IR LOOP
WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 75 KNOTS IS BASED ON
AN OVERALL ASSESSMENT OF DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD
AND REFLECTS THE IMPROVED STRUCTURE OF THE CYCLONE. UPPER LEVEL
ANALYSIS INDICATES THE SYSTEM IS IN AN AREA OF LIGHT VWS WITH GOOD
RADIAL OUTFLOW. TY 01C IS TRACKING ALONG THE SOUTHERN PERIPHERY OF
THE DEEP-LAYERED STR TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY HALOLA WILL CONTINUE TRACKING WEST-NORTHWESTWARD UNDER THE
STEERING INFLUENCE OF THE STR THROUGH TAU 72. IT IS FORECAST TO
INTENSIFY OVER THE NEXT 48 HOURS - PEAKING AT 90 KNOTS - DUE TO
CONTINUED FAVORABLE ENVIRONMENTAL CONDITIONS WITH GOOD OUTFLOW, LOW
VWS, AND SSTS ABOVE 28 CELSIUS. BEYOND TAU 48, VWS WILL INCREASE
WHICH WILL BEGIN TO WEAKEN THE SYSTEM. DYNAMIC MODEL GUIDANCE IS IN
TIGHT AGREEMENT THROUGH TAU 72, LENDING TO HIGH CONFIDENCE IN THIS
PORTION OF THE FORECAST.
   C. IN THE EXTENDED TAUS, THE SYSTEM WILL BEGIN TO TURN POLEWARD
AS IT ROUNDS THE SOUTHWESTERN PERIPHERY OF THE STEERING STR. TY
HALOLA SHOULD CONTINUE TO WEAKEN DUE TO VWS ABOVE 30 KNOTS CAUSED BY
STRONG NORTHERLY FLOW FROM A BUILDING MID-LATITUDE RIDGE TO THE
NORTHWEST, SSTS DROPPING BELOW 26 CELSIUS, THEN LAND INTERACTION WITH
JAPAN. DYNAMIC MODEL GUIDANCE SPREADS OUT AFTER TAU 72 DUE TO VARYING
DEGREES IN THE TIMING OF THE RE-CURVE. THIS FORECAST HAS AGAIN
SHIFTED SLIGHTLY FURTHER WESTWARD FROM THE PREVIOUS FORECAST DUE TO
VARYING MODEL SOLUTIONS IN THE EXTENT OF THE STR TO THE NORTH. THIS
UNCERTAINTY LEADS TO AN OVERALL LOW CONFIDENCE IN THE JTWC
FORECAST.//
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