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Hawaiian Islands Synoptic Discussion and Guidance
315
FXHW60 PHFO 191405
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST SUN MAY 19 2013
.SYNOPSIS...
A LOW ALOFT WILL LINGER NORTHEAST OF THE ISLAND CHAIN PRODUCING
UNSETTLED WEATHER THROUGH MIDWEEK. LOCALLY HEAVY RAIN WILL BE
POSSIBLE TODAY WITH A SLIGHT CHANCE FOR THUNDERSTORMS ON THE BIG
ISLAND. A SHARP TROUGH WILL PRODUCE LIGHT BACKGROUND FLOW RESULTING
IN A LAND AND SEA BREEZE PATTERN NEAR THE SURFACE IN THE SHORT AND
MIDTERM. TRADE WINDS WILL RETURN LATE THIS WEEK.
&&
.DISCUSSION...
A COMPLICATED WEATHER PATTERN PERSISTS ACROSS THE STATE EARLY THIS
MORNING. WATER VAPOR IMAGERY SHOWS A COLD UPPER LOW NORTH OF THE
ISLANDS DIGGING TO THE SOUTHEAST. MEANWHILE...AT THE SURFACE...A
SHARP INVERTED TROUGH HAS AN AXIS ACROSS MAUI AND IS STATIONARY. TO
THE NORTH...A COLD FRONT IS LOCATED ABOUT 75 MILES AWAY FROM KAUAI
AND MOVING SOUTH TOWARDS THE STATE AT 15 MPH. THE FRONT IS BEING
OVERRUN BY BREEZY NORTHERLY WINDS ASSOCIATED WITH HIGH PRESSURE
BEHIND IT.
CURRENT RADAR SHOWS SLOW MOVING SCATTERED SHOWERS DIRECTED IN
NEARLY A COUNTERCLOCKWISE MOTION ACROSS THE ISLAND CHAIN. THIS IS
DUE TO THAT SHARP TROUGH AXIS FOCUSED ON MAUI THIS MORNING. THE
GREATEST AREAL SHOWER COVERAGE IS OFF THE WINDWARD AND SOUTHEAST
COAST OF THE BIG ISLAND...AND THE LEAST COVERAGE AROUND KAUAI.
SOUNDINGS FROM THIS MORNING SHOW WEAK ELEVATION INVERSIONS AT 10
KFT AT LIHUE AND 14 KFT AT HILO...WITH PRECIPITABLE WATER VALUES
OF 1.16 INCHES AT LIHUE AND 1.53 INCHES AT HILO.
THE LIGHT BACKGROUND FLOW RESULTING FROM THE PRESENCE OF THE SURFACE
TROUGH WILL ALLOW SEA BREEZES TO BUILD OVER THE ISLANDS AGAIN TODAY.
KAUAI WILL BE THE EXCEPTION WITH MODERATE NORTHERLY WINDS EXPECTED.
CLOUDS AND SHOWERS ASSOCIATED WITH THE APPROACHING FRONT SHOULD
ARRIVE IN KAUAI LATE THIS MORNING AND AFTERNOON...BEFORE WASHING OUT
OVER OAHU TONIGHT. FOR OAHU AND MAUI COUNTY...THE SEA BREEZES WILL
BRING CLOUDS AND SHOWERS ONTO THE ISLAND INTERIORS AND LEEWARD
SECTIONS THIS AFTERNOON AND EVENING. THE INSTABILITY ALOFT FROM THE
UPPER LOW WILL CAUSE LOCALLY HEAVY RAINFALL ON ALL ISLANDS EXCEPT
KAUAI TODAY...THOUGH CHANCES FOR RAIN WILL REMAIN HIGH ON KAUAI WITH
THE FRONTAL PASSAGE. THE BIG ISLAND WILL ALSO BE A FOCUS FOR CHANCES
OF HEAVY RAIN AND A SLIGHT CHANCE FOR THUNDERSTORMS GIVEN THE POOL
OF NEARBY MOISTURE.
LAND BREEZES WILL SET IN TONIGHT PUSHING MOST OF THE CLOUDS AND RAIN
OFFSHORE LATE. OAHU COULD STILL REMAIN WET TONIGHT AS THAT FRONT
STALLS AND FALLS APART. THE SURFACE TROUGH WILL LINGER NEAR MAUI
THROUGH MONDAY...THEN SLOWLY WEAKEN AND MOVE OFF TO THE WEST.
ALOFT...A LOW WILL PERSIST NORTHEAST OF THE AREA THROUGH MIDWEEK.
LIGHT WINDS ASSOCIATED WITH THE SURFACE TROUGH AND INSTABILITY FROM
THE LOW ALOFT WILL CONTINUE THIS DIURNAL CONVECTIVE PATTERN OVER ALL
THE ISLANDS THROUGH WEDNESDAY...AND INTO THURSDAY FOR SOME LEEWARD
AREAS. THERE IS A POSSIBILITY OF LOCALLY HEAVY SHOWERS ACROSS ISLAND
INTERIORS MONDAY AND TUESDAY GIVEN THE PROXIMITY OF THE UPPER
LOW...BUT NOT VERY CONFIDENT IN TIMING AND LOCATION OF THESE SHOWERS
DUE TO THE COMPLEX SITUATION. WILL HOLD OFF ON PUTTING THIS IN THE
FORECAST FOR NOW.
LONG RANGE MODELS ARE IN GOOD AGREEMENT SHOWING THE TRADE WINDS
BECOMING WELL-ESTABLISHED BY FRIDAY...AND LOCALLY BREEZY NEXT
WEEKEND. THE CONVECTIVE PATTERN WILL END AND THE TRADES WILL BRING
FOCUS LIGHTER SHOWERS TO WINDWARD AND MAUKA AREAS. ANOTHER TROUGH
ALOFT MAY DIG DOWN OVER THE AREA NEXT WEEKEND AND MAY ENHANCE THE
TRADE WIND SHOWERS.
&&
.AVIATION...
COMPLEX WEATHER PATTERN WITH SURFACE TROUGH AXIS NEAR MAUI...WEAK
COLD FRONT MOVING SE TOWARD KAUAI...AND LIGHT WINDS IN PLACE MOST
AREAS. WIDELY SCATTERED AREAS OF MVFR VIS/CIG IN SHRA WILL PERSIST
OVER COASTAL WATERS THROUGH THE PERIOD...WITH SHRA IN GREATEST
CONCENTRATION NEAR THE BIG ISLAND. THE LIGHT WINDS WILL ALLOW
WIDESPREAD SEA BREEZES TO DEVELOP THIS AFTERNOON...WITH CLOUDS AND
+SHRA OVER INTERIOR AND LEEWARD AREAS LEADING TO AREAS OF MVFR
VIS/CIG. ISOL IFR CONDITIONS ARE ALSO POSSIBLE IN AREAS OF +SHRA...
AND IN ISOL +TSRA OVER BIG ISLAND SLOPES THIS AFTERNOON.
DESPITE THE ACTIVE WEATHER PATTERN...VFR CONDITIONS WILL PREVAIL AT
THE TERMINALS...WITH THE EXCEPTION BEING PHNY WHERE MVFR CIG ARE
EXPECTED FROM 20Z-01Z. AIRMET SIERRA FOR MOUNTAIN OBSCURATION IS
CURRENTLY POSTED FOR WINDWARD MAUI...AND WILL LIKELY NEED TO BE
EXPANDED TO INCLUDE MOST OTHER ISLANDS.
&&
.MARINE...
WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY
LEVELS STATEWIDE THIS WEEK. A SERIES OF SWELLS WILL KEEP ELEVATED
SURF ALONG SOUTH FACING SHORES THROUGH MOST OF THE WEEK. SURF IS
EXPECTED TO REMAIN ABOVE THE ADVISORY THRESHOLD THROUGH AT LEAST
EARLY MONDAY MORNING...BUT MAY BE EXTENDED INTO TUESDAY IF
CONDITIONS PERSIST. A MARINE WEATHER STATEMENT REMAINS POSTED FOR
WAVES BREAKING NEAR CHANNEL ENTRANCES AND POSSIBLE HARBOR SURGES.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST MONDAY FOR SOUTH FACING SHORES
OF ALL ISLANDS.
&&
$$
DISCUSSION/MARINE...FOSTER
AVIATION...BIRCHARD
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office
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It was last modified on: Tue, Sep 21 2010 - 2314 UTC
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