Heavy Rain in Hawaii, April 8 to 10, 2008

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HONOLULU HI
822 AM HST TUE APR 8 2008

.UPDATE...
SKIES ARE MOSTLY CLEAR THIS MORNING OVER KAUAI AND OAHU WHILE A
CONVERGENCE AREA IN THE SURFACE FLOW HAS CREATED AN AREA OF
SHOWERS NEAR LANAI AND JUST SOUTH OF MAUI. THESE SHOWERS WILL
CONTINUE TO AFFECT LANAI THROUGH 10 AM. SOUTH AND WEST SHORES OF
MAUI...AND THE ISLAND OF MOLOKAI MIGHT ALSO SEE SOME REMNANT
SHOWERS THIS MORNING.

ON THE BIG ISLAND...SOUTHERLY WINDS JUST ABOVE THE SURFACE ARE
BRINGING THE PLUME FROM THE HALEMAUMAU AND PUU OO VENT TO THE
NORTH. THE PLUME IS MOVING UP AND OVER THE SOUTHEAST RIFT AND THEN
DOWN INTO THE SOUTH HILO DISTRICT WHERE THE PLUME IS SPREADING
THROUGHOUT THE DISTRICT. SOME OF THE PLUME IS ALSO MOVING FARTHER
NORTH INTO THE NORTH HILO DISTRICT AND ALONG THE HAMAKUA COAST.

THE NOCTURNAL INVERSION ABOVE HILO IS LOCATED AT 500 FEET. THIS
INVERSION SHOULD BREAK BETWEEN 9 AND 10 AM ALLOWING PARTICULATES
FROM THE PLUME TO MIX UPWARD...ALLOWING FOR PARTIAL CLEARING.

&&

.SYNOPSIS...
A TROUGH WILL MOVE WEST ACROSS THE ISLANDS TODAY THROUGH WEDNESDAY.
AS THE TROUGH PASSES...SURFACE WINDS WILL WEAKEN AND SHIFT FROM
NORTHEAST TO EAST SOUTHEAST. THE ATMOSPHERE WILL BECOME MORE MOIST
AND UNSTABLE BEHIND THE TROUGH SO CLOUD COVER WILL INCREASE AND
SHOWERS MAY BECOME MORE ACTIVE. TRADE WINDS WILL RETURN LATER IN THE
WEEK. A SHEAR LINE MAY MOVE SOUTH OVER THE ISLANDS DURING THE
WEEKEND BRINGING MORE WIDESPREAD CLOUDS AND SHOWERS.

&&

.PREV DISCUSSION.../ISSUED 400 AM HST TUE APR 8 2008/

A SURFACE TROUGH HAS MOVED WEST OVER THE BIG ISLAND OF HAWAII. THE
COMPUTER MODELS REMAIN IN GOOD AGREEMENT SHOWING THE TROUGH MOVING
WEST AT 15 MPH ACROSS THE ISLANDS...GRADUALLY WEAKENING AS IT GOES.
AS THE TROUGH PASSES...THE SURFACE WINDS WILL WEAKEN AND SHIFT FROM
NORTHEAST TO SLIGHTLY SOUTH OF EAST. THE TROUGH EXTENDS WELL UP INTO
THE ATMOSPHERE AND IS A BIT SHARPER ABOVE THE SURFACE. WINDS WILL
NOT BECOME VERY SOUTHERLY AT THE SURFACE BEHIND THE TROUGH BUT AT
5000 FEET ABOVE THE SURFACE THE WINDS WILL SHIFT FARTHER TO THE
SOUTH. THE TROUGH WILL BRING AN INCREASE IN INSTABILITY AND THE
SOUTHERLY FLOW WILL MAKE THE ATMOSPHERE MORE MOIST...SO SHOWERS MAY
BE A BIT ACTIVE THROUGH THURSDAY NIGHT. WE HAVE ADDED HEAVY SHOWERS
TO THE FORECAST FOR THE BIG ISLAND THIS AFTERNOON AND TONIGHT.

BY THURSDAY...THE SURFACE TROUGH WILL BE WEST OF KAUAI AND
DISSIPATING. WINDS WILL STRENGTHEN AND SHIFT TO A MORE TYPICAL EAST
NORTHEAST DIRECTION. THE PAST FEW RUNS OF THE GLOBAL MODELS HAVE
BEEN IN PRETTY GOOD AGREEMENT SHOWING A SHEAR LINE MOVING SOUTH OVER
THE ISLANDS NEXT WEEKEND. IT LOOKS LIKE A BAND OF CLOUDS AND SHOWERS
ASSOCIATED WITH THE SHEAR LINE MIGHT REACH KAUAI BY SATURDAY MORNING
AND SPREAD DOWN TO THE BIG ISLAND BY SUNDAY NIGHT. HOWEVER...THAT IS
FAR ENOUGH IN THE FUTURE THAT WE CANNOT BE TOO CONFIDENT YET ABOUT
THIS SCENARIO.

DONALDSON

&&

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

&&

MORRISON