AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST MON APR 18 2011

.SYNOPSIS...
A TROUGH PASSING ACROSS THE WESTERN ISLANDS WILL BRING INCREASED
CLOUD COVER BUT FEW ADDITIONAL SHOWERS TODAY. LIGHT EASTERLY WINDS
WILL SPREAD WESTWARD ACROSS THE STATE OVER THE NEXT FEW DAYS AS THE
TROUGH WEAKENS...REMAINING WITH US THROUGH THE REST OF THE WEEK.
HOWEVER...LOCAL LAND AND SEA BREEZES MAY STILL OCCUR ACROSS LEEWARD
AREAS. THE RETURN OF THE LIGHT EASTERLY WINDS WILL BE SUPPORTED BY
RIDGING ALOFT WHICH WILL LIMIT RAINFALL AMOUNTS.

&&

.DISCUSSION...
A SURFACE TROUGH IS PASSING SLOWLY EASTWARD ACROSS THE WESTERN
ISLANDS THIS MORNING...DRAGGING A BAND OF BROKEN TO OVERCAST MIDDLE
AND HIGH CLOUDS WITH IT. WINDS ARE LIGHT EASTERLIES NEAR THE BIG
ISLAND AND ACROSS WATERS SOUTH OF THE SMALLER ISLANDS EAST OF
OAHU...BUT ARE EITHER LIGHT AND VARIABLE OR LIGHT NORTHEASTERLIES
ELSEWHERE. WHILE THE KAUAI RADAR REMAINS INOPERATIVE THIS
MORNING...RADARS FARTHER TO THE EAST SHOW VERY LITTLE SHOWER
ACTIVITY WITHIN HAWAIIAN LOCAL WATERS. OVERNIGHT SOUNDINGS SHOW THE
AIRMASS REMAINS UNSTABLE ACROSS THE WESTERN HALF OF THE MAIN ISLAND
CHAIN...WITH CAPE OVER 1800 J/KG AND OVER 1.7 INCHES OF PRECIPITABLE
WATER NOTED ON THE LIHUE SOUNDING. CONTRAST THIS WITH A CAPE OF
ABOUT 130 J/KG AND JUST OVER AN INCH OF PRECIPITABLE WATER AT HILO
AND ONE CAN SEE HOW CONDITIONS STABILIZE FROM WEST TO EAST.

WE EXPECT THE TROUGH ACROSS THE WESTERN ISLANDS TO SLOWLY DISSIPATE
AND MOVE BACK WESTWARD OVER THE NEXT 24 HOURS. WINDS ARE SLIGHTLY
STRONGER WEST OF THE TROUGH AND MORE NORTHERLY...WITH LIGHTER EAST
TO NORTHEAST WINDS NOTED EAST OF THE TROUGH. WHILE KAUAI MAY BRIEFLY
SEE THESE STRONGER WINDS TODAY AND TONIGHT...LOCAL LAND AND SEA
BREEZES MAY STILL OCCUR ACROSS LEEWARD AREAS. LOCAL LAND AND SEA
BREEZES ARE ALSO EXPECTED ACROSS THE REMAINING ISLANDS TODAY AND
TONIGHT.

GFS CONTINUES TO KEEP WINDS LIGHTER THROUGH THE WEEK THAN PREVIOUSLY
FORECAST...SO WE HAVE FOLLOWED SUIT BY CHANGING THE GRIDDED DATABASE
AND FORECAST. WE NOW EXPECT WINDS TO VEER BACK TO EASTERLIES THROUGH
THE WEEK AS THE TROUGH WANES...BUT WIND SPEEDS WILL LIKELY STAY IN
THE 10 TO 15 KT RANGE. MOST LAND AREAS WILL SEE WINDS AT THE LOW END
OF THIS RANGE...WHILE LEEWARD AREAS MAY NOT BE AFFECTED BY
PREVAILING EASTERLIES AT ALL. EXPECTED RIDGING ALOFT WILL LOWER THE
INVERSION...PUTTING A CAP ON DEEP CONVECTION AND LIMITING RAINFALL.
THIS LIGHT EASTERLY WIND PATTERN IS EXPECTED TO LAST THROUGH THE
REST OF THE FORECAST PERIOD. WE HAVE KEPT A WINDWARD BIAS FOR POPS
GIVEN THE BORDERLINE LOW EASTERLY WINDS WITH LITTLE OR NO BIG
ISLAND BLOCKING THROUGH THE WEEK. GFS SHOWS STRONGER TRADE WINDS
RETURNING THE FOLLOWING WEEK.

&&

.MARINE...
THE WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY
CRITERIA THROUGH AT LEAST FRIDAY.

THE SOUTH FACING SHORES CAN EXPECT A SERIES OF SMALL TO MODERATE
SIZE SWELLS FROM THE SOUTH THROUGH TUESDAY. A LARGER...LONG PERIOD
SOUTH SWELL IS FORECAST TO ARRIVE TUESDAY NIGHT...AND PEAK WEDNESDAY
NIGHT. SURF HEIGHTS PRODUCED BY THIS SWELL WILL LIKELY REACH HIGH
SURF ADVISORY THRESHOLD ALONG SOUTH FACING SHORES AS EARLY AS
WEDNESDAY AFTERNOON. THIS SWELL WILL SLOWLY DECLINE INTO THE WEEKEND.

FOR THE NORTH AND WEST FACING SHORES...THERE WILL BE A SERIES OF
SMALL TO MODERATE SIZE SWELLS FROM THE NORTHWEST THIS WEEK. A
MODERATE SIZE SWELL IS SLATED TO REACH THE ISLANDS TONIGHT AND PEAK
TUESDAY NIGHT. A SMALLER FOLLOW UP SWELL IS SLATED FOR FRIDAY NIGHT.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$