Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 051330
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST TUE MAY 5 2015

.SYNOPSIS...
MODERATE TRADE WINDS WILL START TO INCREASE IN SPEED AFTER
WEDNESDAY...AND PROBABLY PEAK OVER THE WEEKEND. CLOUDS AND SHOWERS
WILL BE MOST ACTIVE OVER WINDWARD SLOPES...THOUGH A FEW MAY DRIFT
LEEWARD AT TIMES...ESPECIALLY AS WIND SPEEDS INCREASE.

&&

.DISCUSSION...
SURFACE OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS STILL REPORTED
SOLIDLY MODERATE TRADE WINDS. THE INVERSION WAS A LITTLE ON THE HIGH
SIDE...AND NOT PARTICULARLY STRONG...LEAVING AMPLE HEADROOM FOR
SHOWERS TO DEVELOP. SOUNDING MEASUREMENTS OF PRECIPITABLE WATER OVER
THE STATE SUGGESTED A RELATIVELY DRY AIR MASS...AND RECENT SATELLITE
ESTIMATES SHOWED THE MOISTER AIR TO THE EAST FOLLOWING A TRAJECTORY
THAT SHOULD PASS NORTH OF KAUAI. LOOSE BANDS OF STRATOCUMULI AND
CUMULI PASSING OVER THE STATE FROM THE EAST PRODUCED FEWER BUT MORE
INTENSE SHOWERS THAN ARE TYPICAL FOR TRADE-WIND CONDITIONS...
POSSIBLY IN RESPONSE TO THE RAISED INVERSION. AS USUAL...INDIVIDUAL
SMALL SHOWERS ALSO CONTINUED TO ENHANCE OVER WINDWARD SLOPES...AND
LIKELY WILL CONTINUE TO DO SO THROUGH THE WEEK.

ALOFT...BROAD ZONAL RIDGING ACROSS MOST OF THE CENTRAL PACIFIC OCEAN
KEPT THE MAIN PART OF THE STORM TRACK WELL TO THE NORTH OF THE
ISLANDS...BUT SHALLOW EXTENSIONS OF PASSING TROUGHS AND RIDGES DID
REACH THE STATE. THESE WAVES...AND THEIR INFLUENCE ON THE
SUBTROPICAL RIDGE AT THE SURFACE...WILL BRING MOST OF THE CHANGES TO
LOCAL WEATHER THROUGH THE WEEK.

RECENT MODEL RUNS CONTINUED TO SHOW DIFFERENCES IN PHASE AMONG THE
PASSING IMPULSES THROUGH ABOUT MID-WEEK. THEY DID SEEM TO AGREE
THAT MID-LEVEL RIDGING SHOULD INCREASE SUBSTANTIALLY FROM THE
NORTHWEST BY LATE IN THE WEEK...POSSIBLY SUPPORTING SIGNIFICANTLY
INCREASED TRADE WINDS OVER THE WEEKEND. THE CURRENT FORECAST
INCLUDED SUCH A TREND...BUT IF THE SOLUTIONS BUILD DEEP RIDGING TO
THE NORTH MUCH MORE...THEN FURTHER INCREASES MAY BE NECESSARY...
INCLUDING PERHAPS A MENTION OF GALES IN THE CHANNELS.

OTHERWISE CLIMATOLOGY MAY PROVE DIFFICULT TO OUTPREDICT.
SIMILARLY...IT MAY BE TEMPTING TO FORECAST TRENDS IN TRADE-WIND
SHOWERS SIMPLY FROM MODEL CONSENSUS PRECIPITABLE WATER...BUT IN
PRACTICE THE CORRELATION TENDS TO BE LESS THAN IDEAL. ADDITIONAL
RUNS SHOULD BE INSTRUCTIVE.

&&

.MARINE...
A SMALL CRAFT ADVISORY REMAINED IN EFFECT FOR TYPICALLY WINDIER
AREAS AROUND MAUI AND THE BIG ISLAND THROUGH MUCH OF THE WEEK.

THE TRADE WINDS ALSO WILL MAINTAIN ELEVATED SHORT-PERIOD SURF ALONG
EAST-FACING SHORES THROUGH THE WEEK...THOUGH HEIGHTS SHOULD REMAIN
BELOW THE ADVISORY THRESHOLD. A LONG-PERIOD SOUTH-SOUTHWEST SWELL
WILL BUILD TODAY...AND THEN PEAK WEDNESDAY INTO THURSDAY...LIKELY
BRINGING ADVISORY-LEVEL SURF TO SOUTH-FACING SHORES. A TINY NORTH
SWELL IS EXPECTED THROUGH WEDNESDAY...AND A SLIGHTLY LARGER
NORTH-NORTHWEST SWELL FROM THURSDAY INTO SATURDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST FRIDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS

&&

$$

RYSHKO





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