Waterspout in Hawaiian Waters, March 1, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST TUE MAR 1 2011

.SYNOPSIS...
A HIGH PRESSURE RIDGE TO THE NORTH WILL MAINTAIN GENTLE TO MODERATE
TRADE WINDS AND FOCUS SHOWERS ACROSS WINDWARD AND MAUKA SECTIONS
THROUGH WEDNESDAY. LOW PRESSURE WILL DEVELOP WEST OF THE STATE...AND
BRING A COLD FRONT TO KAUAI ON FRIDAY. THE FRONT WILL WEAKEN AS IT
MOVES DOWN THE ISLAND CHAIN DURING THE WEEKEND. SHOWERS WILL SPREAD
ACROSS THE STATE AHEAD OF THE FRONT BEGINNING WEDNESDAY NIGHT.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS A RELATIVELY ZONAL PATTERN ACROSS THE
CENTRAL PACIFIC. ONE SHORTWAVE OF NOTE IS LOCATED WELL WEST OF THE
STATE...NEAR 23N162E. AT THE SURFACE...A WEAKENING FRONT IS LOCATED
SOUTHEAST OF THE BIG ISLAND...WITH A WEAK HIGH PRESSURE RIDGE
LOCATED TO THE NORTH OF THE STATE. A SURFACE TROUGH IS LOCATED ABOUT
800 MILES WEST NORTH WEST OF THE STATE. 00Z RAOBS SHOW INVERSIONS
RANGE FROM 5KFT AT LIHUE TO NEAR 8KFT AT HILO. PRECIPITABLE WATERS
ALSO RANGE FROM 0.9 AT LIHUE TO 1.2 AT HILO.

GENTLE TO MODERATE TRADE WINDS WILL CONTINUE INTO WEDNESDAY...
KEEPING SHOWERS FOCUSED ACROSS WINDWARD AND MAUKA SECTIONS. THE
LINGERING MOISTURE NEAR THE BIG ISLAND WILL BEGIN THIN OUT
TONIGHT...ALLOWING THE ENHANCED SHOWERS TO DIMINISH. DESPITE THE
SOLID CLOUD COVER...RADAR IMAGERY AND RAIN GAGES HAVE SHOWN THAT
SHOWERS HAVE DIMINISHED THIS AFTERNOON. PATCHY HIGH CLOUDS WILL BE
PASSING ACROSS THE STATE...BUT WILL BE TRANSIENT AT LEAST TONIGHT
BEFORE THICKENING WEDNESDAY/WEDNESDAY NIGHT.

THE UPPER TROUGH WELL WEST OF THE STATE WILL MOVE EAST AND SHARPEN.
THIS UPPER LEVEL SYSTEM WILL PASS OVER THE SURFACE TROUGH WEST OF
THE STATE...CAUSING LOW PRESSURE TO DEVELOP BY LATE
WEDNESDAY/WEDNESDAY NIGHT. THE 12Z MODELS ARE SIMILAR WITH THE
GENERAL PATTERN...SHOWING THE LOW TRACKING NORTHEAST AND BRINGING A
COLD FRONT ACROSS THE ISLANDS. HOWEVER...THERE CONTINUES TO BE
DIFFERENCES WITH THE DETAILS OF HOW THE PATTERN WILL EVOLVE. THE
ECMWF HAS BEEN RELATIVELY CONSISTENT OVER THE PAST FEW RUNS...AND IS
WEAKER AND ABOUT 18 HOURS FASTER THAN THE GFS IN BRINGING THE FRONT
TO KAUAI /FRIDAY MORNING AS OPPOSED TO LATE FRIDAY NIGHT IN THE
GFS/. THE GFS HAS BEEN BACK AND FORTH WITH ITS SOLUTIONS. A GENERAL
PATTERN APPEARS TO BE THAT THE OFF-HOUR RUNS /06Z AND 18Z/ ARE
FASTER THAN THE 00Z AND 12Z RUNS. TAKEN INDEPENDENTLY...THE 12Z GFS
TRENDED MUCH FASTER THAN THE 00Z RUN...BUT WAS STILL SLOWER THAN THE
06Z RUN. THE 18Z RUN IS ACTUALLY PRETTY SIMILAR IN TIMING TO THE 06Z
RUN...BOTH OF WHICH WERE FASTER THAN THE 12Z RUN. THE CURRENT
FORECAST IS GEARED TOWARD A TIMING SHOWN BY THE 06Z/18Z GFS...WHICH
IS IN BETWEEN THE TIMING OF THE 12Z GFS AND ECMWF.

THE GFS HAS BEEN QUITE VOLATILE AND THE ECMWF HAS BEEN CONSISTENT.
BEYOND THAT...THE FASTER ECMWF SOLUTION SEEMS MORE PREFERRED FROM A
CONCEPTUAL STANDPOINT. WE HAVE A NEARLY ZONAL JET WITH AN AMPLIFYING
SHORTWAVE TRACKING EASTWARD. ONCE THE SHORTWAVE PASSES OVER THE
EXISTING SURFACE TROUGH...IT WILL INVIGORATE CONVECTION ALONG THE
TROUGH...AND THE LATENT HEAT RELEASE WILL HELP TO STRENGTHEN THE
SHORTWAVE AND LEAD TO FURTHER SURFACE DEVELOPMENT. THE GFS MAY BE
OVERDOING THE ENERGY RELEASE AND OVERDEVELOPING THE SURFACE
LOW...WHICH LEADS TO THE SLOWER SOLUTION. THE FEELING IS THAT THE
FASTER/WEAKER ECMWF SOLUTION IS MORE FAVORABLE WITH THIS TYPE OF
DEVELOPING SYSTEM. HAVE NUDGED THE FORECAST TOWARD A FASTER
SOLUTION...BUT DO NOT WANT TO MAKE WHOLESALE CHANGES DUE TO THE
LARGE TIMING UNCERTAINTY.

WINDS ARE EXPECTED TO VEER SOUTHERLY BY THURSDAY...WHICH WILL HELP
TO BRING HIGHER MOISTURE NORTHWARD ACROSS THE STATE. PW VALUES ARE
FORECAST TO CLIMB NEAR 1.8 INCHES...WHICH IS WELL ABOVE NORMAL FOR
THIS TIME OF YEAR. WE DO NOT ANTICIPATE MUCH IN THE WAY OF THUNDER
WITH THIS SYSTEM. IT DEVELOPS AT A RATHER LOW LATITUDE...AND DOES
NOT HAVE A VERY COLD CORE OF AIR ALOFT. HOWEVER...BECAUSE OF THE
MOISTURE AND INSTABILITY THAT IS PRESENT...HAVE MAINTAINED A MENTION
OF HEAVY RAIN FOR KAUAI/OAHU. STRONG SOUTH TO SOUTHWEST WINDS ARE
ALSO EXPECTED THURSDAY/FRIDAY...MAINLY ACROSS THE WESTERN HALF OF
THE STATE. DO NOT ANTICIPATE ANY WIND ADVISORIES AT THIS POINT...
MAINLY DUE TO THE EXPECTATION THAT THE WEAKER ECMWF SOLUTION WILL
VERIFY. HOWEVER...IF THE LOW THAT DEVELOPS IS STRONGER...AREAS ALONG
THE NORTH AND NORTHEAST SECTIONS OF THE ISLANDS MAY NEED AN ADVISORY
DUE TO DOWNSLOPE ACCELERATIONS.

DESPITE THE TIMING DIFFERENCES...BOTH THE GFS AND ECMWF SHOW A
SIMILAR OVERALL PATTERN WITH THE SYSTEM EVOLUTION. THE LOW WILL MOVE
NORTHEAST OF THE STATE...AND THE TRAILING FRONT/TROUGH IS EXPECTED
TO MOVE ACROSS OAHU AND WEAKEN AND DISSIPATE ACROSS MAUI COUNTY.
STRONGER NORTHEAST WINDS WILL FILL IN BEHIND THE TROUGH...AFFECTING
MAINLY KAUAI AND OAHU. THE TROUGH WILL WEAKEN AS IT REACHES MAUI
COUNTY...LEAVING A MODERATE-LEVEL GRADIENT IN PLACE. HINTS OF A
TROUGH WILL LINGER INTO EARLY NEXT WEEK...WITH MORE NORTHEASTERLY
WINDS NEAR KAUAI AND EASTERLY OR EAST-SOUTHEASTERLY WINDS NEAR THE
BIG ISLAND.

&&

.MARINE...
WINDS WILL REMAIN BELOW SMALL CRAFT ADVISORY LEVELS THROUGH
WEDNESDAY NIGHT...BUT WILL BEGIN TO STRENGTHEN AS THEY VEER AROUND
TO THE SOUTH ON THURSDAY. SOUTHERLY WINDS WILL INCREASE...AND REACH
SMALL CRAFT ADVISORY LEVELS OF 25 KNOTS OR GREATER FOR THE WESTERN
HALF OF THE COASTAL WATERS GENERALLY THURSDAY-FRIDAY.

&&

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

&&

BRAVENDER