664
FXHW60 PHFO 212017
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST TUE MAY 21 2013
SYNOPSIS
A WEAKENING LOW TO OUR NORTH AND A TROUGH JUST WEST OF KAUAI WILL
KEEP WINDS LIGHT ACROSS THE STATE...LEADING TO ONSHORE SEA BREEZES
DURING THE DAY AND OFFSHORE LAND BREEZES AT NIGHT. CLOUDS AND
SHOWERS WILL BE FOCUSED ACROSS INTERIOR SECTIONS OF THE ISLANDS
DURING THE AFTERNOON AND EARLY EVENING. AS THE LOW DISSIPATES...HIGH
PRESSURE NORTHEAST OF THE STATE WILL BRING A RETURN TO TRADE WINDS
BEGINNING THURSDAY. TRADES WILL STRENGTHEN THROUGH THE WEEKEND.
DISCUSSION
WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL LOW ABOUT 600 MILES NORTH
NORTHEAST OF THE STATE...WITH AN UPPER TROUGH EXTENDING ABOUT 300
MILES NORTHWEST OF KAUAI. AT THE SURFACE...LOW PRESSURE IS LESS THAN
500 MILES NORTH OF KAUAI...WITH A TROUGH PASSING JUST WEST OF THE
ISLAND. A WEAKENING FRONT IS ALSO NEARLY STATIONARY NORTHEAST OF
MAUI COUNTY AND THE BIG ISLAND. 12Z RAOB SHOW ELEVATED INVERSIONS
NEAR 9-10KFT...WITH A WEAKER INVERSION AT HILO THAN LIHUE.
PRECIPITABLE WATERS ALSO RANGE FROM 1.24 INCHES AT LIHUE TO 1.4
INCHES AT HILO. THIS LINES UP WELL WITH EARLY MORNING MIMIC TOTAL
PRECIPITABLE WATER IMAGERY...WHICH SHOWS HIGHER MOISTURE VALUES EAST
OF OAHU.
WITH THE WEAK SURFACE FEATURES NEARBY...THE PRESSURE GRADIENT ACROSS
THE ISLANDS REMAINS QUITE WEAK. THE PRESSURE DIFFERENCE BETWEEN BUOY
51101 TO THE NORTHWEST OF KAUAI AND BUOY 51003 TO THE SOUTH OF KAUAI
IS AROUND HALF A MILLIBAR...WHICH IS 1MB LESS THAN THE LOW VALUES
OBSERVED YESTERDAY. WIDESPREAD LAND BREEZES FORMED OVERNIGHT...AND
ONSHORE SEA BREEZES ARE ALREADY BEGINNING TO DEVELOP THIS MORNING.
THIS TYPE OF CONVECTIVE PATTERN IS EXPECTED TO CONTINUE THROUGH
WEDNESDAY...WITH AFTERNOON CLOUDS AND SHOWERS AND SOME CLEARING AT
NIGHT. A BAND OF HIGH CLOUDS HAS FILLED IN OVER THE SMALLER ISLANDS
OVER THE PAST FEW HOURS AHEAD OF THE UPPER TROUGH...AND THESE CLOUDS
WILL LIMIT INSOLATION INITIALLY. BASED ON MORNING SOUNDINGS...
CONDITIONS ARE MORE UNSTABLE ACROSS THE EASTERN HALF OF THE STATE.
ADDITIONAL MOISTURE IS LOCATED FARTHER EAST AS WELL...POOLED ALONG
THE DISSIPATING FRONT. HOWEVER...CONVERGENCE ALONG THE WIDESPREAD
SEA BREEZES SHOULD LEAD TO LIKELY POPS ACROSS THE INTERIORS OF THE
ISLANDS THIS AFTERNOON.
THE LOW NORTH OF THE STATE IS EXPECTED TO MOVE WESTWARD AND
DISSIPATE...WITH THE SURFACE TROUGH MOVING FARTHER WEST OF KAUAI.
THE GRADIENT REMAINS LIGHT THROUGH WEDNESDAY...WHICH WILL ALLOW FOR
ANOTHER DAY OF ONSHORE SEA BREEZES AND AFTERNOON CLOUDS AND SHOWERS.
DESPITE OFFSHORE LAND BREEZES TONIGHT...AS MAY SEE CLOUDS LINGER AS
MOISTURE FROM THE FRONT SPREAD WESTWARD OVER THE STATE. THIS
MOISTURE MAY ALSO HELP TO ENHANCE SHOWERS ON WEDNESDAY...DESPITE
MORE STABLE CONDITIONS AND SLIGHTLY LOWER INVERSION HEIGHTS.
HIGH PRESSURE NORTHEAST OF THE STATE WILL REASSERT ITSELF ACROSS THE
ISLANDS BY THURSDAY. AS THIS HIGH MOVES SOUTHWARD AND THE RIDGE
REESTABLISHES ITSELF NORTH OF THE STATE...WE SHOULD SEE
STRENGTHENING TRADE WINDS THROUGH THE WEEKEND. HOWEVER...AN UPPER
LEVEL LOW DEVELOPING TO OUR NORTHEAST WILL HELP TO DESTABILIZE THE
AIRMASS BY THE WEEKEND. WHILE THE LATEST MODEL RUNS SHOW THIS
FEATURE CONFINED TO UPPER LEVELS...WITH TRADES PERSISTING AT THE
SURFACE...IT WILL HELP TO ERODE THE TRADE WIND INVERSION AND ENHANCE
TRADE WIND SHOWERS. THIS PATTERN IS EXPECTED TO LINGER INTO EARLY
NEXT WEEK.
AVIATION
VFR CONDITIONS PREVAIL AT MOST OF THE TAF SITES WITH SOME LOCAL MVFR
OCCURING OVER PHNY. THESE CONDITIONS WILL LIKELY PERSIST THROUGH
MOST OF THE DAY. DAYTIME HEATING WILL CAUSE SOME MVFR CONDITIONS TO
OCCUR MAINLY OVER INTERIOR AREAS THIS AFTERNOON DUE TO CLOUDS AND
SHRA.
MARINE
THE HIGH SURF ADVISORY FOR SOUTH FACING SHORES CONTINUES THROUGH
THIS EVENING FOR THE PERSISTENT LARGE SOUTH SWELL. ELEVATED SURF FOR
SOUTH FACING SHORES WILL LAST AT LEAST THROUGH WEDNESDAY. A
MODERATE WEST-NORTHWEST SWELL IS EXPECTED TO ARRIVE TONIGHT AND PEAK
WEDNESDAY INTO THURSDAY. WHILE THIS SWELL IS LARGER THAN NORMAL FOR
THIS TIME OF YEAR...SURF IS EXPECTED TO REMAIN BELOW ADVISORY
LEVELS FOR NORTH AND WEST FACING SHORES.
TRADE WINDS ARE EXPECTED TO BE STRONG ENOUGH BY THE WEEKEND FOR
SMALL CRAFT WIND CONDITIONS TO DEVELOP OVER THE WINDIER AREAS AROUND
MAUI COUNTY AND THE BIG ISLAND.
HFO WATCHES/WARNINGS/ADVISORIES
HIGH SURF ADVISORY UNTIL 600 PM HST THIS EVENING FOR SOUTH SHORES OF
ALL ISLANDS.
WIND ADVISORY IN EFFECT FOR BIG ISLAND SUMMITS UNTIL 6 PM HST THIS
EVENING.
PUBLIC/MARINE...BRAVENDER
AVIATION...BURKE
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