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Hawaiian Islands Synoptic Discussion and Guidance

163
FXHW60 PHFO 011359
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
359 AM HST FRI AUG 1 2014

.SYNOPSIS...
HIGH PRESSURE FAR NORTH OF THE STATE WILL KEEP TRADE WINDS BLOWING
THROUGH THE WEEKEND AND INTO NEXT WEEK. ENHANCED MOISTURE MOVING
FROM EAST TO WEST ACROSS THE ISLANDS TODAY THROUGH SATURDAY WILL
RESULT IN AN INCREASE IN SHOWERS...WITH LOCALLY HEAVY RAINFALL
POSSIBLE. DRIER AND MORE STABLE WEATHER IS EXPECTED FROM SUNDAY
THROUGH THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
SHOWERS HAVE REMAINED SCATTERED AT MOST ACROSS WINDWARD SECTIONS
DURING THE NIGHT...WITH RAIN GAUGE DATA SHOWING ONLY SPARSE
ACCUMULATIONS AT A FEW SITES. THERE IS AN AREA OF INCREASING
SHOWER COVERAGE BEYOND 40 MILES SOUTHEAST OF THE BIG ISLAND.
SURFACE ANALYSIS DEPICTS AN ELONGATED HIGH PRESSURE RIDGE OVER
THE NORTHEAST PACIFIC OCEAN...AND THE REMNANT LOW OF FORMER
TROPICAL DEPRESSION GENEVIEVE CENTERED ABOUT 500 MILES SOUTH
SOUTHEAST OF HILO. MODERATE TO LOCALLY BREEZY TRADE WINDS PREVAIL
ACROSS THE STATE. MIMIC-TPW SATELLITE IMAGERY INDICATES A
SIGNIFICANT MOISTURE GRADIENT OVER THE AREA...WITH ESTIMATED PWATS
OVER 2 INCHES BETWEEN 150W AND THE BIG ISLAND...RANGING DOWN
TO AROUND 1.4 INCHES FROM OAHU TO KAUAI. THE 12Z SOUNDINGS INDICATE
THIS MOISTURE GRADIENT AS WELL. THE INVERSION AT HILO HAS RISEN
TO OVER 8000 FEET...BUT REMAINS NEAR 7000 FEET AT LIHUE. ALOFT...
A WEAK MID/UPPER LEVEL TROUGH EXTENDS FROM NEAR 30N160W SOUTHWARD
TO THE WEST OF KAUAI...AND A MID LEVEL RIDGE AXIS EXTENDS WESTWARD
ALONG 20N TO NEAR THE BIG ISLAND.

THE BAND OF DEEP TROPICAL MOISTURE INITIALLY JUST EAST OF THE BIG
ISLAND WILL CONTINUE MOVING WESTWARD ACROSS THE STATE FROM TODAY
THROUGH SATURDAY. THIS TROPICAL MOISTURE SHOULD PEAK THIS AFTERNOON
AND EVENING ACROSS THE BIG ISLAND...THEN LATE TONIGHT THROUGH
SATURDAY MORNING ACROSS THE SMALLER ISLANDS. MODERATE INSTABILITY
WILL BE IN PLACE...BUT THE RISK FOR THUNDERSTORMS WOULD SEEM TO
BE QUITE LOW DUE TO RELATIVELY WARM MID LEVEL TEMPERATURES AND A
LACK OF DEEP FORCING. WITH ONLY A WEAK UPPER TROUGH LIFTING OUT
TO OUR WEST AND NORTH DURING THIS TIME...IT APPEARS THAT THIS WILL
PROBABLY BE MORE OF AN OROGRAPHICALLY DRIVEN EVENT WITH LOCALLY
HEAVY RAINS MOST LIKELY ON THE WINDWARD AREAS...IN CONTRAST TO THE
MORE WIDESPREAD HEAVY RAINS AND THUNDERSTORMS THAT WERE OBSERVED A
COUPLE OF WEEKS AGO WHEN A PREVIOUS BOUT OF TROPICAL MOISTURE
MOVED THROUGH THE STATE. THE FLASH FLOODING THREAT APPEARS TO BE
LOW...BUT WOULD NOT BE SURPRISED TO SEE SOME FLOOD ADVISORIES
ISSUED FROM LATER TODAY THROUGH SATURDAY. FOR THE FORECAST...HAVE
INCLUDED THE MENTION OF LOCALLY HEAVY RAIN FOR THE BIG ISLAND AND
WINDWARD MAUI TODAY...SPREADING WESTWARD TO OAHU THIS EVENING...
KAUAI LATE TONIGHT...AND STATEWIDE SATURDAY MORNING. THE MOISTURE
PLUME SHOULD CONTINUE MOVING WESTWARD SATURDAY...WITH THE HEAVY
RAIN THREAT DIMINISHING FOR ALL AREAS EXCEPT KAUAI COUNTY BY
AFTERNOON.

A GRADUAL DRYING TREND IS EXPECTED FOR SATURDAY NIGHT THROUGH
SUNDAY...THEN A RATHER DRY MODERATE TRADE WIND PATTERN SHOULD
PREVAIL FROM MONDAY THROUGH AT LEAST THE MIDDLE OF NEXT WEEK...
WITH GENERALLY BELOW NORMAL PWATS AND RATHER STRONG RIDGING ALOFT
PREVAILING. WOULD EXPECT LIMITED TRADE SHOWERS ACROSS WINDWARD AND
MAUKA AREAS...MAINLY DURING THE NIGHT AND EARLY MORNING HOURS...
WITH MOSTLY CLEAR AND DRY CONDITIONS LEEWARD.

LOOKING FURTHER AHEAD TOWARD THURSDAY AND FRIDAY OF NEXT WEEK...
THE 00Z MODEL SUITE...AS HAS BEEN THE CASE FOR THE PAST SEVERAL
CYCLES...BRINGS YET ANOTHER SURGE OF DEEP TROPICAL MOISTURE TOWARD
THE STATE FROM THE EAST. THIS MOISTURE APPEARS TO BE ASSOCIATED
WITH THE MODEL DEPICTION OF CURRENT EAST PACIFIC TROPICAL STORM
ISELLE. IT IS HIGHLY UNCERTAIN AT THIS POINT WHETHER REMNANTS OF
THIS SYSTEM WILL MAKE IT TO THE VICINITY OF HAWAII...BUT THERE IS
SOME POTENTIAL FOR ANOTHER BOUT OF WET WEATHER TOWARD THE END OF
NEXT WEEK.

&&

.AVIATION...
INCREASING TROPICAL MOISTURE IS NOW ARRIVING ALONG THE WINDWARD BIG
ISLAND. THE ARRIVAL OF THIS ENHANCED MOISTURE WILL PRODUCE ABUNDANT
LOW CLOUDS AND SHOWERS WITH LOWER CEILINGS AND REDUCED VISIBILITIES.
THESE CONDITIONS WILL REQUIRE THE CONTINUATION OF AIRMET SIERRA FOR
MOUNTAIN OBSCURATION ALONG THE WINDWARD FACING TERRAIN OF THE BIG
ISLAND THROUGH MOST OF THE DAY. AS THIS ENHANCED TROPICAL MOISTURE
CONTINUES TO ADVECT WESTWARD...THESE LOWER CEILINGS AND REDUCED
VISIBILITIES WILL ALSO LIKELY SPREAD TO PARTS OF WINDWARD MAUI LATER
THIS MORNING...SO EXPECT PORTIONS OF MAUI TO BE ADDED TO AIRMET
SIERRA IN THE NEAR FUTURE.

WEST OF MAUI...VFR CONDITIONS ARE EXPECTED TO PREVAIL ACROSS MOST
LEEWARD SECTIONS OF THE OTHER SMALLER ISLANDS THIS MORNING...WITH
BRIEF MVFR CONDITIONS DEVELOPING ALONG WINDWARD FACING SLOPES AND
THE HIGHER TERRAIN ON MOST OF THESE ISLANDS. LATER IN THE DAY...
THERE IS A GOOD CHANCE MOUNTAIN OBSCURATION MAY EVENTUALLY DEVELOP
WEST OF MAUI...SO AIRMET SIERRA MAY ALSO BE REQUIRED FOR ADDITIONAL
PARTS OF THE STATE.

AS A RESULT OF THE MODERATE TO LOCALLY BREEZY LOW-LEVEL TRADE WIND
FLOW...AIRMET TANGO REMAINS IN EFFECT FOR LOW-LEVEL TURBULENCE BELOW
7 KFT IMMEDIATELY SOUTH THROUGH WEST OF THE HIGHER TERRAIN ON ALL
ISLANDS. BASED ON THE LATEST GUIDANCE...THIS AIRMET WILL LIKELY
REMAIN IN EFFECT THROUGH TONIGHT.

&&

.MARINE...
AN 0738Z ASCAT PASS ACROSS THE FAR WESTERN HAWAIIAN COASTAL
WATERS FOUND SOME 20 KNOT WINDS IN THE KAUAI CHANNEL. THE PASS
MISSED THE EASTERN WATERS AROUND MAUI COUNTY AND THE BIG
ISLAND...BUT RECENT HIGH RESOLUTION WRF MODEL DATA SUGGEST THAT 25
KNOT WINDS ARE QUITE POSSIBLE IN THAT AREA. WILL MAINTAIN THE
EXISTING SMALL CRAFT ADVISORY THROUGH SUNDAY.

MODERATE SSW SWELL WILL INCREASE SOMEWHAT THIS AFTERNOON...THEN A
REINFORCING SOUTH SWELL SHOULD INCREASE SURF FURTHER ON
SATURDAY...POSSIBLY APPROACHING OR REACHING MINIMAL ADVISORY
LEVELS ON SOUTH FACING SHORES. THIS SURF EVENT SHOULD PEAK DURING
SATURDAY THEN SLOWLY DECREASE SUNDAY THROUGH MONDAY. SURF WILL
SEE A BUMP ON WEST FACING SHORES AS WELL DUE TO THE SSW DIRECTION.
OTHERWISE...PREVAILING TRADE WINDS WILL CONTINUE TO PRODUCE SHORT
PERIOD SWELL AND CHOPPY NEAR AVERAGE SURF ALONG EAST FACING SHORES
THROUGH THE NEXT SEVERAL DAYS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST SUNDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...HOUSTON




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