Heavy Rain in Hawaii, June 4, 2003

HAWAIIAN ISLANDS SYNOPTIC DISCUSSION AND GUIDANCE
NATIONAL WEATHER SERVICE HONOLULU HI
10 AM HST WED JUN 4 2003

SUMMARY...A LIGHT WIND PATTERN WITH INCREASING CONVECTIVE
SHOWERS...SOME LOCALLY HEAVY...WILL BE AFFECTING THE ISLANDS THROUGH
THE REMAINDER OF THIS WEEK. TRADE WINDS ARE EXPECTED TO MAKE A
GRADUAL RETURN THIS WEEKEND AND THE EARLY PART OF NEXT WEEK AND
BECOME QUITE STRONG BY MIDWEEEK.

DISCUSSION...THE HAWAIIAN ISLANDS CONTINUE TO BE SITUATED IN A COL
REGION WHERE A TROUGH FROM THE NORTH INTERSECTS A WEAK EAST/WEST
RIDGE. THE CYCLONIC VORTICITY ASPECTS OF THE TROUGH WITHIN THIS COL
ARE BEGINNING TO OVERPOWER THE ANTICYCLONIC RIDGE EFFECTS AS THE
TROUGH DIGS STRONGLY TOWARD THE ISLANDS FROM THE NORTH AND
NORTHWEST. THUS INSTABILITY AND MOISTURE AVAILABILITY HAS BECOME
MODIFIED TO THE POINT WHERE SOME MEANINGFUL SHOWERS WILL BE OCCURING
IN OUR VICINITY. SMALL CHANGES IN TEMPERATURE BETWEEN OCEAN AND LAND
AREAS WILL HELP DETERMINE WHERE THESE SHOWERS WILL OCCUR. OUR SEA
SURFACE TEMPERATURES HAVE RISEN TO 28C OR 82F DURING THIS PERIOD OF
LIGHT WINDS AS A FAIRLY THIN UPPER LAYER OF THE OCEAN HAS WARMED SO
THAT NOW THE DEPARTURES FROM NORMAL ARE A SIZEABLE 2 DEGREES C OR 4
DEGREES F WARMER THAN TO BE EXPECTED THIS TIME OF THE YEAR. THIS
WARM WATER AREA IS CENTERED NEAR OR JUST WEST OF KAUAI AND OAHU.
WARMER THAN NORMAL WATER MEANS INCREASED EVAPORATION AND THUS
INCREASED DEWPOINT TEMPERATURES. THESE INCREASES IN LOW LEVEL
MOISTURE AND HEATING FROM BELOW...LATENT AND SENSIBLE HEATING...WILL
AFFECT STABILITY AND MOVE THE ATMOSPHERE TOWARD INSTABILITY AND
POSSIBLE SHOWER DEVELOPMENT.  WE SEE SIGNS OF THAT HAPPENING ON
KAUAI NIIHAU AND OAHU THIS AFTERNOON WHERE LOCALLY HEAVY SHOWERS
ARE OCCURING. A FEW SPOTTY SHOWERS ARE ALSO OCCURING AT THIS TIME
ON ALL OF THE ISLANDS OF MAUI COUNTY INCLUDING KAHOOLAWE. THE BIG
ISLAND WILL ALSO LIKELY RECEIVE SOME SHOWERS THIS LATE AFTERNOON
AND IF NOT TODAY THEN ALMOST CERTAINLY TOMORROW AND FRIDAY.

RIDGING FROM HIGH PRESSURE NEAR THE ALASKA PANHANDLE WILL BUILD
SOUTHWARD AND SOUTHWESTWARD TOWARD THE ISLANDS OVER THE WEEKEND AND
EARLY NEXT WEEK. THIS WILL CUT OFF THE THREAT OF HEAVY SHOWERS AND
RETURN US TO A MORE NORMAL TRADE WIND REGIME. BY WEDNESDAY THE
TRADES SHOULD BE QUITE STRONG.

.HFO...WATCHES......NONE
.      WARNINGS.....NONE
.      ADVISORIES...URBAN AND SMALL STREAM FLOOD ADVISORY FOR
PORTIONS OF OAHU.