Tropical Storm ONE Advisory Sat Jul 18

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01C (HALOLA)
WARNING NR 32//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 01C (HALOLA), LOCATED APPROXIMATELY 920
NM EAST-SOUTHEAST OF IWO TO, HAS TRACKED WESTWARD AT 09 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS ELONGATED, EXPOSED LOW-LEVEL CLOUD LINES WRAPPING INTO AN
ILL-DEFINED CENTER WITH FORMATIVE BANDING DISPLACED NORTH AND SOUTH
OF THE CENTER. MSI ALSO SHOWS A WELL-DEFINED MID-LEVEL CIRCULATION
CENTER NEAR 17.6N 157.3E, WHICH IS DISPLACED OVER THE EASTERN
PERIPHERY OF THE SYSTEM. IR IMAGERY INDICATES CLOUD TOP TEMPERATURES
RANGING FROM -12C TO -15C ASSOCIATED WITH THE MID-LEVEL CIRCULATION
CENTER. A 172341Z METOP-B 89 GHZ IMAGE REVEALS A BROAD LOW-LEVEL
CIRCULATION CENTER WITH CONVECTIVE BANDING OVER THE SOUTHERN SEMI-
CIRCLE WITH SIGNIFICANT DRY AIR WEST OF THE SYSTEM. A 172343Z ASCAT
IMAGE SHOWS AN ELONGATED CIRCULATION WITH 25 TO 30 KNOT WINDS, WHICH
SUPPORTS THE CURRENT INTENSITY ASSESSMENT OF 30 KNOTS. BASED ON THE
WEAK OVERALL STRUCTURE, THERE IS FAIR CONFIDENCE IN THE CURRENT
POSITION. UPPER-LEVEL ANALYSIS INDICATES A MARGINAL ENVIRONMENT DUE
TO THE CLOSE PROXIMITY OF A TUTT CELL NEAR 22N 160E, WHICH IS
PRODUCING CONVERGENT FLOW OVER THE NORTHERN SEMI-CIRCLE AND WESTERLY
VERTICAL WIND SHEAR. TD 01C IS TRACKING ALONG THE SOUTHERN PERIPHERY
OF THE DEEP-LAYERED STR.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TD 01C WILL CONTINUE TRACKING WESTWARD TO WEST-NORTHWESTWARD
UNDER THE STEERING INFLUENCE OF THE STR THROUGH TAU 72. AVAILABLE
DYNAMIC GUIDANCE IS IN TIGHT AGREEMENT WITH A SPREAD OF 60 NM AT
TAU 72, THEREFORE HIGH CONFIDENCE IN THE JTWC FORECAST TRACK THROUGH
TAU 72. TD 01C IS STRUGGLING DUE TO THE MARGINAL UPPER-LEVEL
ENVIRONMENT AND POSSIBLE DRY AIR ENTRAINMENT, THEREFORE, THE SYSTEM
IS FORECAST TO MAINTAIN INTENSITY THROUGH TAU 12 WITH A SLOW RATE OF
INTENSIFICATION FROM TAU 12 TO 48. DUE TO THE WEAK NATURE OF THE
SYSTEM AND THE STRONG LOW-LEVEL STR, THE SYSTEM IS EXPECTED TO
MAINTAIN A GENERALLY WESTWARD TRACK THROUGH TAU 24. THEREAFTER, THE
SYSTEM SHOULD TURN MORE WEST-NORTHWESTWARD AS IT INTENSIFIES AND
BECOMES BETTER ORGANIZED. FORECAST GUIDANCE INDICATES MARGINAL
CONDITIONS THROUGH, AT LEAST, TAU 48; HOWEVER, THERE IS UNCERTAINTY
IN THE INTENSITY FORECAST DUE TO THE COMPLEX INTERACTION WITH THE
TUTT.
   C. IN THE EXTENDED FORECAST PERIOD, EXPECT A MORE WEST-
NORTHWESTWARD TO NORTHWESTWARD TRACK AS THE SYSTEM BEGINS TO
APPROACH THE WESTERN PERIPHERY OF THE STR. DYNAMIC MODEL GUIDANCE
DIVERGES SIGNIFICANTLY WITH THE MESO-SCALE MODELS SHOWING A SHARPER
NORTHWESTWARD TURN THAN THE GLOBAL MODELS, WHICH SHOW A MORE WEST-
NORTHWESTWARD TRACK. THERE IS A 320-NM SPREAD IN SOLUTIONS AT TAU
120, THEREFORE, UNCERTAINTY IS HIGH AND CONFIDENCE IN THE JTWC
FORECAST TRACK IS LOW. INTENSIFICATION IS MORE LIKELY DUE TO
IMPROVED POLEWARD OUTFLOW WITH A PEAK INTENSITY OF 80 KNOTS FORECAST
AT TAU 96.//
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