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Hawaiian Islands Synoptic Discussion and Guidance

616
FXHW60 PHFO 250635
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
835 PM HST THU APR 24 2014

.SYNOPSIS...
BREEZY TRADE WINDS WILL PREVAIL TONIGHT THROUGH SATURDAY...WEAKEN
SUNDAY AND MONDAY...THEN RECOVER BY THE MIDDLE OF NEXT WEEK AS
HIGH PRESSURE TO OUR NORTH FLUCTUATES IN STRENGTH. CLOUDS AND
SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS THROUGH THE FORECAST
PERIOD...WITH SOME SPILLOVER INTO LEEWARD SECTIONS.

&&

.DISCUSSION...
RADAR LOOPS AND RAIN GAUGE DATA INDICATE A TYPICAL MODERATE TRADE
REGIME PREVAILING...WITH SCATTERED LOW-TOPPED SHOWERS BRINGING
LIGHT TO LOCALLY MODERATE RAINFALL AMOUNTS TO WINDWARD AND MAUKA
AREAS...AND SOME SHOWERS MOVING ACROSS INTO LEEWARD AREAS. THE
00Z SOUNDINGS SHOWED RELATIVELY WEAK AND HIGH INVERSIONS BASED
FROM 7000 TO 8500 FEET ACROSS THE STATE...WITH AMPLE LOW LEVEL
MOISTURE PRESENT BENEATH THE INVERSIONS. AT THE SURFACE...A 1029
MB HIGH IS CENTERED ABOUT 1000 MILES NNE OF HONOLULU...WITH A
RIDGE EXTENDING WSW TO MIDWAY AND BEYOND. ALOFT...AREAS OF HIGH
CLOUDINESS ARE STREAMING ACROSS HAWAII...TO THE EAST OF A WEAK
UPPER TROUGH LOCATED BETWEEN 170W AND THE DATELINE. MIMIC-TPW
SATELLITE IMAGERY AND MODEL DATA INDICATE THAT AN AREA OF SOMEWHAT
HIGHER MOISTURE WILL CONTINUE MOVING WESTWARD THROUGH THE STATE
DURING THE REST OF TONIGHT INTO FRIDAY MORNING...AND THEREFORE
EXPECT HIGH RAIN CHANCES TO PERSIST ACROSS WINDWARD/MAUKA AREAS
WITH A GOOD DEAL OF SPILLOVER INTO LEEWARD. THE EXISTING FORECAST
APPEARS TO BE ON TRACK IN THE NEAR TERM AND NO UPDATES ARE
PLANNED.

FRIDAY THROUGH SATURDAY...HIGH PRESSURE TO OUR NORTH WILL SINK
SLOWLY SOUTHWARD WHILE REMAINING NEAR 1030 MB STRENGTH...CAUSING
TRADES TO INCREASE ACROSS THE STATE. A BUILDING MID LEVEL RIDGE TO
THE NORTH SHOULD STRENGTHEN AND LOWER INVERSIONS DURING THIS TIME
AS WELL. WIND GUSTS ABOVE 40 MPH WILL BE LIKELY ACROSS THE
TYPICALLY FAVORED DOWNSLOPE AND HEADLAND/RIDGE LOCATIONS...AND
ISOLATED GUSTS OVER 50 MPH WILL BE POSSIBLE. WILL EVALUATE LATER
TONIGHT TO DETERMINE IF WIND ADVISORIES MAY BE NEEDED FOR ANY
ZONES ON FRIDAY. OTHERWISE...WITH A LOWERING INVERSION AND
SOMEWHAT DRIER AIRMASS SPREADING IN FROM THE EAST WOULD EXPECT
LIMITED WINDWARD/MAUKA SHOWER ACTIVITY...ALTHOUGH THE FAIRLY
STRONG TRADES WILL CONTINUE TO ALLOW SPILLOVER INTO SOME LEEWARD
AREAS.

SUNDAY THROUGH MONDAY...A PATTERN CHANGE SEEMS LIKELY TO OCCUR
WITH A DEEP MID/UPPER TROUGH DEVELOPING ACROSS THE CENTRAL
PACIFIC. THIS WILL SUPPORT A SURFACE COLD FRONT WHICH WILL ADVANCE
SOUTHEASTWARD TO THE NORTH OF THE STATE. THE FRONT APPEARS
UNLIKELY TO MAKE IT THIS FAR SOUTH...BUT WILL CAUSE THE TRADES TO
WEAKEN CONSIDERABLY. SEABREEZES MAY BE ABLE TO DEVELOP ALONG WITH
A CONVECTIVE CLOUD/SHOWER PATTERN ACROSS MANY SECTIONS OF THE
STATE ON MONDAY AFTERNOON.

LOOKING FURTHER AHEAD...MODERATE TRADES SHOULD RESUME TUESDAY...
AS THE REMNANTS OF THE FRONTAL BOUNDARY OR SHEAR LINE WASH OUT
ACROSS THE STATE. HIGH PRESSURE BEHIND THIS BOUNDARY SHOULD THEN
MAINTAIN MODERATE TO FRESH TRADES THROUGH THE MIDDLE PART OF NEXT
WEEK...WITH TYPICAL WINDWARD/MAUKA SHOWERS PREVAILING.

&&

.AVIATION...
PASSING SHOWERY LOW CLOUDS WILL BRING TEMPO MVFR CONDITIONS...MAINLY
TO WINDWARD AND MAUKA SECTIONS.

AIRMET TANGO REMAINS POSTED FOR LOW LEVEL TURBULENCE BELOW 8000
FEET TO THE LEE OF THE MOUNTAINS DUE TO THE BREEZY TRADE WINDS. IT
WILL REMAIN IN EFFECT UNTIL FURTHER NOTICE.

&&

.MARINE...
A SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL WATERS IN ANTICIPATION
OF STRENGTHENING WINDS AND BUILDING COMBINED SEAS THROUGH SATURDAY
AFTERNOON. NORTHEASTERLY WINDS WILL REACH THEIR MINIMUM SPEEDS LATE
SUNDAY INTO MONDAY AS THE RIDGE TO OUR NORTH WEAKENS...AND THEN
INCREASE AGAIN TUESDAY THROUGH THE MIDDLE OF NEXT WEEK.

PERSISTENT TRADE WINDS WILL BUILD SEAS...PRODUCING ROUGH SURF NEAR
OR JUST BELOW ADVISORY LEVELS ALONG EAST-FACING SHORES FROM
FRIDAY INTO SATURDAY. SEAS WILL DIMINISH WITH THE WINDS LATE
SATURDAY AND SUNDAY.

A SMALL NORTHWEST SWELL WILL CONTINUE TO PRODUCE WELL BELOW
ADVISORY LEVEL SURF ALONG EXPOSED SHORES OF THE SMALLER ISLANDS
THROUGH FRIDAY. THIS SWELL WILL DECREASE SATURDAY...THEN ANOTHER
SMALL NORTHWEST SWELL MAY ARRIVE LATE SUNDAY AND CONTINUE THROUGH
TUESDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST SATURDAY FOR ALL HAWAIIAN
WATERS.

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...KINEL




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