Hail and Damaging Wind in Hawaii, December 19 to 20, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST SAT DEC 19 2009

.SYNOPSIS...
A DRY NORTHEASTERLY TRADE WIND FLOW WILL PERSIST ACROSS MOST OF THE
STATE THROUGH THE WEEKEND...WHILE WINDWARD BIG ISLAND MAY EXPERIENCE
ENHANCED RAINFALL DUE TO MOISTURE LEFT BEHIND BY A DISSIPATED FRONT.
WINDS WILL DECREASE DURING THE FIRST HALF OF NEXT WEEK AS A
WEAKENING FRONT APPROACHES FROM THE NORTHWEST. LITTLE RAINFALL IS
EXPECTED FROM THIS FRONT. ANOTHER FRONT MAY IMPACT THE STATE LATE IN
THE WEEK.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL SHORTWAVE TROUGH JUST
MOVING EAST OF THE BIG ISLAND. A SHORTWAVE RIDGE IS LOCATED NEAR
KAUAI...AHEAD OF A SECOND UPPER TROUGH ABOUT 600 MILES NORTHWEST OF
THE STATE. CONVECTION ASSOCIATED WITH THE SHORTWAVE NEAR THE BIG
ISLAND HAS WEAKENED DURING THE MORNING...WITH CLOUD TOPS WARMING AND
LIGHTNING STRIKES DIMINISHING. THE AIRMASS ACROSS THE SMALLER
ISLANDS IS MUCH MORE STABLE THAN THE AIRMASS NEAR THE BIG ISLAND.
THE 12Z SOUNDING FROM HILO SHOWS NO INVERSION AND A MOISTURE DEPTH
IN EXCESS OF 14000 FT...AND A 500MB TEMPERATURE OF -16C. THE
SOUNDING FROM LIHUE SHOWS A STABLE INVERSION NEAR 5000 FT WITH A
PRECIPITABLE WATER OF 0.7 INCHES.

THE MOISTURE NEAR THE BIG ISLAND IS A RESULT OF A FRONT THAT
DISSIPATED YESTERDAY. THE AMSU/SSMI BLENDED TOTAL PRECIPITABLE WATER
IMAGERY SHOWS PW VALUES OF UP TO 1.5 INCHES EXTENDING TO THE EAST
NORTHEAST AND TO THE SOUTHWEST OF THE BIG ISLAND. THIS MOISTURE WILL
LINGER THROUGH THE WEEKEND. THE SECOND SHORTWAVE NORTHWEST OF THE
STATE WILL DIG SOUTHEASTWARD...REACHING THE SMALLER ISLANDS TONIGHT
AND CROSSING THE BIG ISLAND ON SUNDAY. GIVEN THE DRY AND STABLE
AIRMASS ACROSS THE WESTERN HALF OF THE STATE...THIS SHORTWAVE IS
EXPECTED TO HAVE LITTLE IMPACT ON SENSIBLE WEATHER. LIGHT SHOWERS
WILL BE CONFINED TO WINDWARD AND MAUKA SECTIONS. HOWEVER...AS THE
SHORTWAVE REACHES THE MOISTURE POOLED ACROSS THE EASTERN HALF OF THE
STATE...IT WILL SPAWN ADDITIONAL SHOWERS AND POSSIBLE THUNDERSTORMS
NEAR THE BIG ISLAND AGAIN LATE TONIGHT/SUNDAY MORNING. MOST ACTIVITY
WILL BE FOCUSED ACROSS WINDWARD SECTIONS AND WINDWARD COASTAL
WATERS...SIMILAR TO THE ACTIVITY EARLY THIS MORNING.

DRY CONDITIONS WILL CONTINUE ACROSS THE STATE BEHIND THE SHORTWAVE
THROUGH EARLY NEXT WEEK. THE AIRMASS WILL MOISTEN SLIGHTLY...BUT
STILL REMAIN DRIER THAN NORMAL. TRADE WINDS WILL CONTINUE...AND
LIGHT SHOWER ACTIVITY WILL BE FOCUSED ACROSS WINDWARD AND MAUKA
AREAS. WINDS WILL STEADILY WEAKEN THROUGH MONDAY. A WEAKENING FRONT
WILL STALL NORTHWEST OF THE STATE ON TUESDAY AND WEDNESDAY. THIS
FRONT MAY BE SOME ADDITIONAL SHOWERS TO KAUAI AND OAHU....BUT IS NOT
EXPECTED TO BE SIGNIFICANT. HOWEVER...IT WILL SHIFT THE RIDGE
SOUTHWARD ACROSS THE STATE...LEADING TO LIGHT WINDS AND A RATHER DRY
LAND AND SEA BREEZE PATTERN BY WEDNESDAY. A STRONGER FRONT IS
EXPECTED TO APPROACH THE STATE THURSDAY/FRIDAY. WHILE IT WILL BE
WEAKENING AS WELL...IT SHOULD HAVE ENOUGH OF A PUSH TO MAKE IT DOWN
THE ISLAND CHAIN.

&&

.MARINE...
A FAST-MOVING LOW NORTH OF THE STATE PRODUCED A NORTH SWELL THAT
WILL AFFECT US THROUGH THE WEEKEND. SEAS AT THE WAIMEA BAY BUOY
HAVE REACHED 11 FT...AND THE KAILUA BUOY HAS BEEN HOVERING AROUND
9-10 FT. BECAUSE THE LOW WAS RELATIVELY CLOSE TO THE STATE...THE
SEAS HAVE A FRESH 12 SECOND PERIOD. THIS WILL KEEP SURF BELOW
ADVISORY LEVELS FOR NORTH FACING SHORES...BUT WILL BRING SURF TO
ADVISORY LEVELS FOR ANY EACH FACINGS SHORES THAT ARE EXPOSED TO A
NORTH SWELL. THE SWELL MAY ALSO PRODUCE MODERATE SURGES IN NORTH
FACING HARBORS SUCH AS KAHULUI AND HILO. A SMALL CRAFT ADVISORY IS
ALSO IN EFFECT FOR HAZARDOUS SEAS.

A LARGER NORTHWEST SWELL MAY PRODUCE SURF AROUND WARNING LEVELS FOR
NORTH AND WEST FACING SHORES DURING THE MIDDLE OF NEXT WEEK. THE
SYSTEM THAT WILL SEND THE FRONT TOWARD THE ISLANDS DURING THE END
OF NEXT WEEK MAY ALSO DELIVER AN EVEN LARGER NORTHWEST SWELL LATE IN
THE WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FOR EAST FACING SHORES OF ALL ISLANDS EXCEPT
LANAI AND KAHOOLAWE THROUGH SUNDAY AFTERNOON.

SMALL CRAFT ADVISORY THROUGH TONIGHT FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-KAUAI CHANNEL-
OAHU WINDWARD WATERS-KAIWI CHANNEL-MAUI COUNTY WINDWARD WATERS-
ALENUIHAHA CHANNEL-BIG ISLAND WINDWARD WATERS.

&&

BRAVENDER