Heavy Snow in Hawaii, February 11 to 13, 2001

HAWAIIAN ISLANDS SYNOPTIC DISCUSSION AND GUIDANCE
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST SAT FEB 10 2001

SUMMARY...A VERY MOIST AND UNSTABLE AIR MASS REMAINS OVER THE
HAWAIIAN ISLANDS. THE WESTERN PART OF THE ISLAND CHAIN NEAR KAUAI
CONTINUES TO BE THE MOST UNSTABLE AND SOME HEAVY SHOWERS ARE PRESENT
OVER THE WATERS ABOUT 50 MILES TO THE SOUTH OF THAT ISLAND. HIGH
CLOUDS FROM CONVECTION IN THE TROPICS COVERS MUCH OF BIG ISLAND AND
MAUI.

DISCUSSION...AN INVERTED TROUGH IN THE SURFACE EASTERLIES HAS MOVED
JUST WEST OF THE ISLANDS WHERE IT NOW IS STATIONARY WITH EAST
SOUTHEAST WINDS PRESENT OVER THE ISLANDS FEEDING INTO THIS TROUGH
WHICH IS JUST WEST OF 160W. MEANWHILE HIGH PRESSURE BUILDING TO THE
NORTHWEST OF THE ISLANDS NEAR 40N 170W IS CAUSING A SURGE IN
NORTHEASTERLY SURFACE WINDS SPREADING TOWARD THE ISLANDS AND CAUSING
THE INVERTED TROUGH TO COME BACK EASTWARD INTO THE ISLAND CHAIN WITH
A SHEARLINE OR FRONTAL BAND ALONG ITS NORTHWEST SIDE WHERE THE
NORTHEAST WINDS ARE SURGING. THE INVERTED TROUGH IS FORECAST TO BE
OVER THE CENTRAL ISLANDS DURING THE FIRST HALF OF THE WORK WEEK IF
NOT LONGER WITH LIGHT SOUTHEAST WINDFS OVER THE BIG ISLAND END OF
THE CHAIN AND GUSTY NE WINDS WITH FREQUENT SHOWERS OVER THE KAUAI
END. THUS NOT TOO PLEASANT A WEATHER PATTERN FOR THE WESTERN
ISLANDS.

THE PRESENT INDISTINCT PATTERN WITH A NUMBER OF SMALL CYCLONIC AND
ANTICYCLONIC VORTICES MILLING AROUND IN A MOIST AND UNSTABLE
ATMOSPHERE WITHIN THE LARGER TROUGH IS A TOUGH ONE TO FATHOM.
PRESSURES HAVE BEEN FALLING OVER OUR AREA AT LARGE WHICH SUGGESTS
THAT THERE IS AN INCREASED THREAT OF LOCALIZED HEAVY SHOWERS
BREAKING OUT WITHIN THESE SMALLER CYCLONIC VORTICES AS THEY MOVE
OVER THE ISLANDS. THE LIHUE SOUNDING POINTS OUT THAT THE GREATEST
DANGER OF THIS HAPPENING IS OVER THE WESTERN ISLANDS. THE FAIRLY
STRONG NEAR SURFACE ESE WINDS SUGGEST THAT THERE IS NOT MUCH OF A
PREFERENCE AS TO WHETHER CONVECTION WILL FORM OVER LAND VS SEA
DURING THE NIGHT. IF ANYTHING LAND AREAS WITH TERRAIN DIFFERENCES
MAY ACTUALLY INVITE SHOWERS TO CLING ON TO THIS ISLAND TERRAIN...
THUS THE NEED FOR A FLASH FLOOD WATCH.  ROSENDAL

.PHFO.....WARNINGS.....NONE
.         WATCHES......FLASH FLOOD KAUAI
.         ADVISORIES...SMALL CRAFT ADVISORY MAUI EASTWARD
.                      HIGH SURF ADVISORY EAST SHORES