Flash Flood Warning 8, NWS Honolulu, HI

HAWAIIAN ISLANDS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST TUE FEB 1 2005

.SYNOPSIS...
THE AIRMASS REMAINS MOIST AND UNSTABLE AHEAD OF A SLOW MOVING COLD
FRONT IN THE KAUAI CHANNEL. AN UPPER LEVEL DISTURBANCE PASSING NEAR
THE ISLANDS TONIGHT AND WEDNESDAY IS EXPECTED TO ENHANCE SHOWERS AND
THUNDERSTORMS...AND SO THE RISK FOR EXCESSIVE RAINFALL CONTINUES
THROUGH WEDNESDAY. A TROUGH BOTH AT THE SURFACE AND ALOFT WILL
LINGER NEAR THE ISLANDS THROUGH THE LATTER HALF OF THIS
WEEK...KEEPING THE WEATHER A BIT UNSETTLED. TRADE WINDS WILL FINALLY
RETURN TO THE ISLANDS THIS WEEKEND AS HIGH PRESSURE PASSES TO OUR
NORTH.

&&

.DISCUSSION...
THOUGH NOT MUCH IN THE WAY OF RAIN TODAY...THINGS ARE BEGINNING TO
PICK UP AROUND THE HAWAIIAN ISLANDS AS AN UPPER LEVEL SHORTWAVE
BEGINS TO MAKE ITS PRESENCE KNOWN. ISOLATED HEAVY SHOWERS AND/OR
THUNDERSTORMS FORMED OVER AND AROUND THE ISLANDS RIGHT AROUND SUNSET
TODAY...AND CONTINUE TO POP UP ALMOST AT RANDOM THIS EVENING.
BELIEVE THIS TREND WILL CONTINUE THROUGH THE EVENING...WITH SHOWERS
AND THUNDERSTORMS INCREASING LATE TONIGHT INTO WEDNESDAY AS THE
SHORTWAVE WE ARE WATCHING GETS CLOSER AND EVENTUALLY MOVES OVER THE
ISLANDS. THE SHORTWAVE IS WELL DEFINED IN WATER VAPOR IMAGERY AND
APPEARS WELL HANDLED BY THE MODELS. THE AXIS OF THE SHORTWAVE IS
CURRENT LOCATED ROUGHLY ALONG A LINE BETWEEN 25N166W AND
14N169W...NEARLY 400 MILES WEST OF KAUAI AT ITS CLOSEST POINT.
ENHANCED SHOWERS ARE NOTED DIRECTLY BELOW AND JUST AHEAD OF THE
SOUTHERN HALF OF THE SHORTWAVE AXIS...AT THE MOMENT WELL TO THE
SOUTHWEST OF THE STATE. HOWEVER...THE SHORTWAVE IS EXPECTED TO COZY
UP TO KAUAI AND DEEPEN THE EXISTING TROUGH OVER THE STATE. WHEN
THIS DEEPENING OCCURS TOMORROW...A GOOD AREA OF DIFLUENCE WILL SET
UP OVER EASTERN HALF OF THE STATE...OPENING THE DOORS FOR INCREASED
SHOWERS AND THUNDERSTORMS. IF THE CURRENT RELATIONSHIP BETWEEN THE
SHORTWAVE AXIS AND THE ENHANCED SHOWERS HOLDS THROUGH TOMORROW...THE
HEAVIEST SHOWERS AND THUNDERSTORMS MAY REMAIN OVER WATER SOUTHWEST
OF THE STATE. AGREE WITH THE CURRENT FORECAST PHILOSOPHY KEEPING
SLIGHT CHANCE OF THUNDERSTORMS FOR MAUI COUNTY AND THE BIG ISLAND
WEDNESDAY WILL LET THE CURRENT PACKAGE STAND FOR NOW.

.PREVIOUS DISCUSSION...
THE TROUGH IS IN NO HURRY TO LEAVE THE ALOHA STATE. THE MODELS
LINGER THIS FEATURE OVER THE ISLANDS FOR THE REST OF THE WEEK...AND
MOST MODELS DEVELOP AN UPPER LEVEL LOW TO THE NORTH OR NORTHEAST OF
THE ISLANDS. DEEPER MOISTURE WILL LINGER NEAR THE BIG ISLAND...BUT A
RELATIVELY DRIER AIRMASS IS EXPECTED TO OVERSPREAD AT LEAST THE
WESTERN MAIN ISLANDS FOR WEDNESDAY AND BEYOND AS TRADES TRY TO BUILD
IN. BEST RAIN CHANCES WILL REMAIN NEAR THE BIG ISLAND...BUT EVEN THE
SMALLER ISLANDS WILL SEE PASSING SHOWERS...SOME COULD BE BRIEFLY
HEAVY...WITH THE UPPER TROUGH AND ITS SURFACE REFLECTION NEARBY.

THE UPPER TROUGH IS FINALLY EXPECTED TO SLIDE FARTHER EAST BY THE
WEEKEND...WITH MODEL CONSENSUS GIVING A HIGH OF ABOUT 1024 MB OR SO
PASSING NORTH OF THE ISLANDS NEAR 33N. THIS SHOULD RETURN TRADE
WINDS AND MUCH MORE SETTLED WEATHER FOR THE WEEKEND INTO NEXT
WEEK...ASIDE FROM MAINLY WINDWARD AND MAUKA SHOWERS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FOR OAHU MOLOKAI LANAI MAUI KAHOOLAWE AND THE BIG
ISLAND THROUGH WEDNESDAY.

WINTER WEATHER ADVISORY FOR BIG ISLAND SUMMITS THROUGH WEDNESDAY.

&&

TANABE