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Hawaiian Islands Synoptic Discussion and Guidance

469
FXHW60 PHFO 241957
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST THU JUL 24 2014

.SYNOPSIS...
TRADE WINDS REMAIN LOCALLY BREEZY TODAY...THEN DIMINISH SLIGHTLY
DURING THE UPCOMING WEEKEND. BRIEF WINDWARD SHOWERS WILL CONTINUE
FOR THE NEXT COUPLE DAYS...THEN INCREASE OVER THE WEEKEND AND INTO
EARLY NEXT WEEK.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL HIGH JUST SOUTHWEST OF THE
STATE...WITH A RIDGE EXTENDING OVER THE ISLANDS. A COMPACT UPPER LOW
IS LOCATED FAR NORTHWEST OF THE STATE. AT THE SURFACE...HIGH
PRESSURE IS LOCATED FAR NORTH-NORTHEAST OF THE STATE...WITH A TROUGH
FAR TO THE NORTHWEST. 12Z SOUNDINGS SHOW A STRENGTHENING INVERSION
LESS THAN 6KFT AT LIHUE...SOMEWHAT HIGHER AT HILO. PRECIPITABLE
WATERS RANGE FROM 1.3 INCHES AT LIHUE TO NEAR 1.5 INCHES AT HILO.
EARLY MORNING MIMIC TOTAL PRECIPITABLE WATER IMAGERY SHOWS DRIER AIR
WITH TPW VALUES AROUND 1 INCH JUST NORTHEAST OF THE STATE. HIGHER
TPW VALUES ARE LOCATED OVER 300 MILES NORTHEAST OF THE STATE...AS
WELL AS SEVERAL HUNDRED MILES EAST OF THE BIG ISLAND.

REPORTS FROM RAIN GAGES ACROSS THE STATE OVERNIGHT AND THIS MORNING
SHOW THE GREATEST RAINFALL OCCURING OVER WINDWARD BIG ISLAND...WITH
LOWER AMOUNTS ACROSS THE SMALLER ISLANDS. THIS IS IN LINE WITH THE
APPROACH OF THE DRIER AIR SEEN IN SATELLITE TPW AND THE MORE STABLE
CONDITIONS OBSERVED IN THE LIHUE SOUNDING. CONDITIONS WILL BECOME
DRIER AND MORE STABLE ACROSS THE BIG ISLAND AS WELL TODAY. TRADE
WINDS WILL REMAIN GUSTY FOR ANOTHER DAY...BEFORE DIMINISHING
SLIGHTLY AS WE HEAD INTO THE WEEKEND. THE TRADES WILL KEEP SHOWERS
FOCUSED ACROSS MAINLY WINDWARD AND MAUKA AREAS...AND MOST PREVALENT
DURING THE NIGHT AND EARLY MORNING. THE POCKET OF MOISTURE NORTHEAST
OF THE STATE WILL MOVE THROUGH TONIGHT...MAINLY BRUSHING BY KAUAI.

AS WE HEAD THROUGH THE WEEKEND...THE UPPER TROUGH NORTHWEST OF THE
STATE WILL GRADUALLY MOVE SOUTHEAST...PASSING JUST NORTH OF THE
ISLANDS. A WEAK SURFACE REFLECTION ASSOCIATED WITH THIS UPPER TROUGH
MAY WEAKEN THE GRADIENT SOMEWHAT ACROSS THE ISLANDS. HOWEVER...
POTENTIAL DEVELOPING SYSTEMS PASSING FAR SOUTH OF THE STATE MAY
INSTEAD TIGHTEN THE PRESSURE GRADIENT ACROSS THE ISLANDS. THE POCKET
OF MOISTURE FAR EAST OF THE STATE IS CURRENTLY LOCATED NEAR 140W.
GFS 850-700MB MOISTURE DOES A REASONABLE JOB DEPICTING THIS
AREA...AND BRINGS IT TO THE BIG ISLAND EARLY SATURDAY. THIS IS A
LITTLE FASTER THAN CURRENTLY DEPICTED IN THE FORECAST...WHICH MAY
NEED TO BE ADJUSTED.

EXTENDED MODELS SHOW THE POTENTIAL FOR ANOTHER SURGE OF TROPICAL
MOISTURE APPROACHING THE STATE FROM THE SOUTHEAST BY THE MIDDLE OF
NEXT WEEK. TIMING IS STILL UNCERTAIN...BUT MAY NOT BE UNTIL THE
WEDNESDAY/THURSDAY TIME FRAME. THIS MOISTURE WILL HELP TO ENHANCE
TRADE WIND SHOWERS ONCE MORE.

&&

.AVIATION...
AIRMET TANGO FOR LOW LEVEL TURB TO THE LEE OF TERRAIN WILL REMAIN IN
PLACE FOR THE REST OF 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 TEMPO MOUNTAIN OBSC OVER THE WINDWARD BIG
ISLAND THROUGH THE MORNING. VFR CONDITIONS WILL PREVAIL ELSEWHERE
DURING THE DAY...WITH ISOL MVFR CIGS EXPECTED OVER WINDWARD AREAS.

&&

.MARINE...
A SMALL CRAFT ADVISORY REMAINS IN EFFECT TODAY FOR THE TYPICALLY
WINDIER WATERS AROUND THE BIG ISLAND AND MAUI. WINDS MAY BE SLOWER
TO DIMINISH THAN ANTICIPATED...AND WE MAY NEED TO EXTEND THE
ADVISORY ONCE MORE. WINDS ARE EXPECTED TO INCREASE FURTHER ON SUNDAY
AND INTO EARLY NEXT WEEK AS A DEVELOPING SYSTEM PASSING WELL SOUTH
OF THE STATE HELPS TO TIGHTEN THE PRESSURE GRADIENT.

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 SOUTHERN
HEMISPHERE...WHILE SHORT PERIOD WIND WAVES FROM THE EAST REPRESENT
THE ONLY SOURCE OF SWELL FROM THE NORTHERN HEMISPHERE.

&&

.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...BRAVENDER
AVIATION...FOSTER



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