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Hawaiian Islands Synoptic Discussion and Guidance

011
FXHW60 PHFO 241333
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST THU JUL 24 2014

.SYNOPSIS...
TRADE WINDS REMAIN MODERATE TO LOCALLY BREEZY TODAY...THEN
DIMINISHING SLIGHTLY DURING THE UPCOMING WEEKEND. BRIEF WINDWARD
SHOWERS WILL CONTINUE DURING THE NEXT COUPLE OF DAYS...THEN WINDWARD
SHOWERS WILL INCREASE TOWARDS THE LATER PART OF THE WEEKEND AND INTO
EARLY NEXT WEEK.

&&

.DISCUSSION...
A SFC HIGH FAR NNE OF THE MAIN HAWAIIAN ISLANDS IS KEEPING A
MODERATE TO LOCALLY STRONG TRADE WIND PATTERN ACROSS THE ALOHA STATE
WITH SHOWERS FOCUSING OVER WINDWARD AND MOUNTAIN AREAS. DURING THE
OVERNIGHT HOURS...RADAR DATA SHOWED SEVERAL SMALL BANDS OF MOISTURE
STREAMING ACROSS THE ISLANDS FROM THE E WITH THE MOST ACTIVE SHOWERS
BEING OBSERVED OVER THE KOOLAU MOUNTAINS IN OAHU...THE WINDWARD AND
SE SLOPES OF HALEAKALA IN MAUI...AND THE W MAUI MOUNTAINS. ALTHOUGH
ACCUMULATIONS REMAIN LOW...PERSISTENCE OF THESE SHOWERS OVER THE
SAME LOCATIONS COULD PRODUCE SOME MINOR FLOODING ISSUES THROUGH THE
REST OF THE EARLY MORNING HOURS.

BY MID MORNING TODAY...THE AIRMASS OVER THE ISLANDS WILL START TO
GRADUALLY BECOMING DRIER...ALONG WITH ATMOSPHERIC CONDITIONS
BECOMING MORE STABLE. 12Z SOUNDINGS FROM LIHUE AND HILO SHOW THAT
THE INVERSIONS ARE RE-ESTABLISHING AROUND 6-8 THOUSAND FEET...ALONG
WITH A DEVELOPING RIDGE ALOFT. THIS SYNOPTIC SCENARIO WILL FAVOR A
DECREASE IN SHOWER ACTIVITY DURING THE NEXT SEVERAL DAYS.

LATEST MIMIC/GLOBAL MODEL MOISTURE ANALYSES DEPICT A DRIER AIRMASS
UPSTREAM OF THE ISLANDS WHICH IS EXPECTED TO BRING A MORE TYPICAL
TRADE WIND REGIME FOR THE SEASON...DOMINATED BY WINDWARD SHOWERS
FAVORING NIGHTS AND MORNINGS...AND PERIODS OF AFTERNOON CLOUDS AND
SHOWERS OVER THE LEEWARD AREAS OF THE BIG ISLAND DURING THE NEXT
COUPLE OF DAYS. THEN BY LATE SAT AND INTO SUN...MODELS SHOW A WEAK
LOW MOVING S OF THE ISLANDS AND BRINGING A SMALL INCREASE IN SHOWER
ACTIVITY...ALONG WITH POTENTIAL FOR STRONGER TRADES. THIS SCENARIO
WILL ALSO BE REINFORCED BY THE DEVELOPMENT OF WEAK TROUGHING ALOFT
AND INCREASING MOISTURE CONTENT AT THE LOW LVLS LATE IN THE WEEKEND
AND INTO EARLY NEXT WEEK.

LONG RANGE MODELS ARE ALSO DEPICTING A LARGE AREA OF TROPICAL
MOISTURE REACHING THE ISLANDS FROM THE E SOMETIME ON TUE. AND
ALTHOUGH IS TOO EARLY TO EMBRACE A DEFINITE SOLUTION FOR THE
EXTENDED FORECAST PERIOD...THE SITUATION WILL BE CLOSELY MONITORED
WITH THE FORECAST BEING ADJUSTED AS NEW MODEL DATA BECOMES
AVAILABLE.

&&

.AVIATION...
AIRMET TANGO FOR LOW LEVEL TURB TO THE LEE OF TERRAIN WILL REMAIN IN
PLACE TODAY. RADAR VAD WIND PROFILES SHOW 20 TO 25 KT LOW LEVEL
WINDS WITH THE INVERSION SITTING BETWEEN 6000 TO 8000 FT. MODELS
SHOW LITTLE CHANGE IN LOW LEVEL WINDS THROUGH THE AFTERNOON.

AIRMET SIERRA IS UP FOR MOUNTAIN OBSC OVER WINDWARD MAUI AND THE BIG
ISLAND. MAUI SHOULD BE DROPPED BEFORE SUNRISE...BUT THE BIG ISLAND
AIRMET WILL REMAIN UP THROUGH AT LEAST THE FIRST PART OF THE
MORNING. AS THE MOISTURE IN THE TRADE FLOW IS SET TO CLEAR THE OTHER
ISLANDS SOON...VFR WILL PREVAIL ELSEWHERE DURING THE DAY...WITH
ISOL MVFR CIGS EXPECTED OVER WINDWARD AREAS.

&&

.MARINE...
A SMALL CRAFT ADVISORY REMAINS IN EFFECT THROUGH TODAY FOR THE
TYPICALLY WINDIER WATERS AROUND THE BIG ISLAND AND MAUI. WINDS ARE
EXPECTED TO DIMINISH BELOW SCA SPEEDS FRIDAY THROUGH SATURDAY.
WINDS WILL THEN INCREASE SLIGHTLY ON SUNDAY AND INTO EARLY NEXT WEEK
AS A TROPICAL SYSTEM PASSING WELL S OF THE ISLANDS AND BRINGS
TIGHTER PRESSURE GRADIENTS.

NO SIGNIFICANT SWELLS ARE EXPECTED THROUGH THE UPCOMING WEEK. SMALL
LONG-PERIOD BACKGROUND SWELL FROM THE SSW AND SHORT-PERIOD SWELL
FROM THE SE REPRESENT THE SWELL SOURCES FROM THE S HEMISPHERE...
WHILE SHORT PERIOD WIND WAVES FROM THE E REPRESENT THE ONLY SOURCE
OF SWELL FROM THE N HEMISPHERE. THE OAHU SURF DISCUSSION /SRDHFO/
HAS BEEN UPDATED AND CONTAINS DETAILS THAN CAN BE LOOSELY APPLIED
STATEWIDE.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY THROUGH 6 PM HST TODAY FOR THE PAILOLO
AND ALENUIHAHA CHANNELS...MAALAEA BAY AND WATERS SOUTH OF THE BIG
ISLAND.

&&

$$

DISCUSSION/MARINE...REYNES
AVIATION...WROE





Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office