Flash Flood Warning 159, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST THU NOV 2 2006

.SYNOPSIS...
AN UPPER LEVEL DISTURBANCE PASSING NEAR THE ISLANDS TODAY WILL KEEP
THE THREAT FOR LOCALLY HEAVY RAINFALL AWHILE LONGER. THE WEATHER
WILL BE MORE SETTLED AS WE HEAD INTO THE WEEKEND...BUT LIGHT WINDS
AND ABUNDANT MOISTURE WILL MAKE FOR HUMID CONDITIONS AND SCATTERED
SHOWERS. RAINFALL WILL TEND TO FAVOR THE INTERIOR OF THE ISLANDS
DURING THE AFTERNOONS FOR FRIDAY THROUGH MONDAY. THE TRADES ARE
EXPECTED TO BUILD BACK OVER THE ISLANDS WITH LESS HUMID WEATHER
STARTING TUESDAY.

&&

.DISCUSSION...
RAIN CONTINUES ACROSS THE MAIN HAWAIIAN ISLANDS...BUT OVERALL WE ARE
SEEING A DOWNWARD TREND. THE SHORTWAVE IS STILL ON TRACK TO MOVE
OVERHEAD...AND THAT COMBINED WITH THE SATURATED CONDITIONS MEANS
THAT THE THREAT OF FLOODING STILL EXISTS. AT 9 AM...ANOTHER BATCH OF
RAIN WAS JUST BEGINNING TO MOVE ON SHORE OF OAHU...WHICH PROMPTED A
FLOOD ADVISORY ISSUANCE.

NO CHANGES IN THE FORECAST PHILOSOPHY AT THIS TIME. PREVIOUS
DISCUSSION FOLLOWS.

&&

.PREV DISCUSSION...
ISSUED 400 AM
WATER VAPOR IMAGERY EARLY THIS MORNING IS SHOWING AN UPPER LEVEL
SHORTWAVE ABOUT 300 MILES WEST-NORTHWEST OF KAUAI THAT IS
APPROACHING THE ISLANDS. THIS FEATURE IS HELPING TO ENHANCE SHOWERS
OVER OAHU AND MAUI COUNTY EARLY THIS MORNING. AS THE UPPER LEVEL
DISTURBANCE PASSES TO THE NORTH OF THE ISLANDS...THE DEEP LAYER
FORCING WHICH HAS BEEN RESPONSIBLE FOR THE HEAVY RAINFALL WILL SHUT
DOWN...GIVING WAY TO FEWER SHOWERS FOR THE AFTERNOON FOR MOST
LOCALES. THE AIRMASS WILL REMAIN MOIST AND MARGINALLY UNSTABLE...SO
EVEN INTO THE AFTERNOON A FEW LOCALLY HEAVY SHOWERS ARE POSSIBLE
MAINLY FOR MAUI COUNTY AND THE BIG ISLAND.

THE SUMMITS OF HALEAKALA...MAUNA KEA...AND MAUNA LOA ARE SANDWICHED
BETWEEN THE MID LEVEL DISTURBANCE TO THE WNW AND RIDGING DEVELOPING
TO THE SOUTH OF THE ISLANDS. THE TIGHT PRESSURE GRADIENT BETWEEN
THESE TWO FEATURES HAS CAUSED WINDS TO REACH WARNING LEVELS AT THE
HIGHEST ELEVATIONS OF THE BIG ISLAND...AND ADVISORY LEVELS AT THE
SUMMIT OF HALEAKALA. MODEL GUIDANCE SHOWS THE WINDS UP THERE WILL
RELAX ONCE THE DISTURBANCE STARTS TO MOVE AWAY LATER TODAY.

THE SUBTROPICAL RIDGE IS EXPECTED TO REDEVELOP NEAR THE BIG ISLAND
LATE THIS WEEK. THIS WILL KEEP MOST OF THE MAIN HAWAIIAN ISLANDS IN
CONVERGENT SOUTH OR SOUTHWEST FLOW THROUGH THE WEEKEND. ALTHOUGH THE
MODELS SHOW DECREASING MOISTURE ALOFT...THE LOW AND MID LEVELS WILL
REMAIN RATHER MOIST WITH BOTH THE GFS AND WRF SHOWING PRECIPITABLE
WATER STAYING NEAR 1.75 INCHES EVEN INTO THE WEEKEND. THIS SUGGESTS
WE COULD STILL SEE SOME SMALL BANDS OF SHOWERS COMING AT THE SMALLER
ISLANDS FROM THE SOUTH. OTHERWISE...WE WILL SETTLE INTO A CONVECTIVE
PATTERN FOR FRIDAY THROUGH SUNDAY THAT SHOULD FOCUS CLOUDS AND
RAINFALL OVER THE ISLAND INTERIORS DURING THE AFTERNOONS AND
EVENINGS. OVERALL THE WEATHER WILL BE MUCH MORE SETTLED FOR MOST
PLACES. FOR FRIDAY...I HAVE LIMITED THE MENTION OF LOCALLY HEAVY
RAINFALL TO JUST THE INTERIOR OF THE BIG ISLAND DURING THE AFTERNOON.

EARLY NEXT WEEK THE MODELS STILL ARE TRYING TO BUILD A HIGH TO THE
NORTH AND NORTHEAST OF THE ISLANDS. THAT WILL EVENTUALLY ALLOW
TRADES TO WORK BACK OVER THE ISLANDS DURING THE EARLY PART OF THE
NEXT WORK WEEK. THE GRIDS SHOW A TRANSITION ON TUESDAY BACK TOWARD A
MORE CLIMATOLOGICALLY FAVORED WINDWARD/MAUKA SHOWER REGIME...
STARTING FOR MAUI AND THE BIG ISLAND ON TUESDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH THIS AFTERNOON FOR NIIHAU...KAUAI...OAHU...
MOLOKAI...LANAI...KAHOOLAWE...AND MAUI.

HIGH WIND WARNING UNTIL 4 PM HST THIS AFTERNOON FOR BIG ISLAND
SUMMITS.

WIND ADVISORY UNTIL 4 PM HST THIS AFTERNOON FOR HALEAKALA SUMMIT.

&&

M BALLARD