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WindNNE 11 mph
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Hawaiian Islands Synoptic Discussion and Guidance

360
FXHW60 PHFO 290624
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
824 PM HST THU APR 28 2016

.SYNOPSIS...
A STRONG RIDGE NORTH OF THE AREA WILL KEEP TRADE WINDS LOCALLY
BREEZY THROUGH FRIDAY. SLIGHT WEAKENING OF THE TRADES IS POSSIBLE
FRIDAY NIGHT AND SATURDAY AS A WEAK FRONT PASSES FAR NORTH OF THE
STATE...THEN A NEW HIGH WILL BUILD IN TO OUR NORTH SUNDAY AND
MONDAY WITH TRADES STRENGTHENING ONCE AGAIN. THE TRADES WILL
FOCUS SHOWERS PRIMARILY OVER WINDWARD SLOPES. SOME SHOWERS WILL
SPREAD LEEWARD OVER THE SMALLER ISLANDS...MAINLY NIGHTS AND
MORNINGS. AFTERNOON SHOWERS ARE POSSIBLE OVER THE LEE SLOPES OF
THE BIG ISLAND.

&&

.DISCUSSION...
TRANQUIL TRADE WIND WEATHER PREVAILS ACROSS HAWAII ON THIS
THURSDAY EVENING. RADAR SHOWS ISOLATED LIGHT SHOWERS MOVING EAST
TO WEST WITHIN THE TRADE FLOW...WITH RAIN GAUGE DATA SHOWING
ALMOST ALL LAND STATIONS REMAINING DRY DURING THE PAST SEVERAL
HOURS. SURFACE ANALYSIS DEPICTS A 1030 MB HIGH CENTERED ABOUT 1400
MILES NE OF PHNL...WITH A RIDGE EXTENDING WESTWARD TO THE NORTH
OF THE STATE...AND A COLD FRONT FAR TO THE NW NEAR MIDWAY ATOLL.
ALOFT...A MID/UPPER LEVEL RIDGE IS CENTERED A FEW HUNDRED MILES
NE OF THE STATE...WITH A VERY DRY/STABLE AIRMASS OVER HAWAII.
MIMIC-TPW SATELLITE IMAGERY SHOWS A GENERALLY DRY AIRMASS OVER AND
AROUND THE STATE...WITH ESTIMATED PWATS AROUND 1 INCH. THE 00Z
SOUNDINGS ALSO SHOW A DRY AND STABLE AIRMASS IN PLACE...WITH PWATS
RANGING FROM 1 TO 1.2 INCHES AND STRONG INVERSIONS BASED AROUND
7500 TO 8000 FEET.

OVERNIGHT...EXPECT SHOWERS TO INCREASE...MAINLY ACROSS WINDWARD
AREAS...AS A BAND OF CLOUDS MOVES IN FROM THE EAST. WHILE MANY
WINDWARD AREAS WILL EXPERIENCE THESE PASSING SHOWERS...RAINFALL
AMOUNTS SHOULD REMAIN MOSTLY LIGHT. THE EXISTING FORECAST APPEARS
TO BE IN GOOD SHAPE...AND NO UPDATES ARE PLANNED FOR THIS EVENING.

LITTLE CHANGE TO THE ONGOING TRADE WIND WEATHER PATTERN IS
EXPECTED THROUGH THE NEXT SEVERAL DAYS. BREEZY TRADES WILL PERSIST
ON FRIDAY AS THE RIDGE HOLDS FIRM TO OUR NORTH...THEN SHOULD
WEAKEN SLIGHTLY FRIDAY NIGHT INTO THE WEEKEND DUE TO THE WEAK
COLD FRONT CURRENTLY NEAR MIDWAY PASSING BY WELL TO OUR NORTH.
A NEW HIGH IS THEN FORECAST TO BUILD NORTH OF THE STATE SUNDAY
THROUGH MONDAY...WHICH WILL CAUSE TRADE WINDS TO INCREASE ONCE
AGAIN. SHOWERS AND CLOUDS WILL CONTINUE TO FAVOR MAINLY WINDWARD
SECTIONS...ESPECIALLY DURING THE NIGHT AND EARLY MORNING HOURS.
THERE WILL ALSO BE THE CHANCE FOR SCATTERED SHOWERS EACH AFTERNOON
AND EARLY EVENING ON THE KONA SLOPES. PERSISTENT RIDGING ALOFT
WITH ONLY SHALLOW MOISTURE AVAILABLE WILL KEEP MOST OF THE SHOWER
ACTIVITY ON THE LIGHT SIDE.

AS THE SURFACE HIGH SHIFTS SLOWLY EASTWARD TO OUR NORTH NEXT
WEEK...MODELS SHOW MOISTURE FROM THE DISSIPATED FRONTAL REMNANTS
GETTING CAUGHT UP IN THE TRADE WIND FLOW AND EVENTUALLY MOVING
SW ACROSS THE ISLANDS. THE LATEST GFS HAS COME INTO BETTER
AGREEMENT WITH THE EARLIER ECMWF RUN ON THE TIMING OF THIS...
SHOWING THE STRIPE OF ENHANCED MOISTURE REACHING THE STATE
TUESDAY AFTERNOON AND MOVING ACROSS THE AREA THROUGH WEDNESDAY.
WILL AWAIT ADDITIONAL MODEL RUNS TO CONFIRM THIS FASTER TIMING
BEFORE MAKING ANY ADJUSTMENTS TO THE EXISTING FORECAST.

&&

.AVIATION...
MODERATE TO FRESH TRADE WINDS WILL FOCUS CLOUDS AND LIGHT SHOWERS
OVER THE WINDWARD AND MAUKA AREAS. AIRMET TANGO REMAINS IN EFFECT
FOR TEMPO MODERATE LOW LEVEL TURB OVER AND IMMEDIATELY S THROUGH W
OF THE MOUNTAINS DUE TO THE TRADES. CONDITIONS ARE EXPECTED TO
PERSIST THROUGH TONIGHT AND POSSIBLY FRIDAY AS WELL.

TEMPO MVFR CIGS MAY DEVELOP LATE TONIGHT ALONG WINDWARD SLOPES AND
COASTS. AN AIRMET FOR MTN OBSCURATION MAY BECOME NECESSARY FOR EAST
FACING SLOPES LATE NIGHT OR EARLY FRIDAY.

&&

.MARINE...
THE LATE MORNING ASCAT PASS ALONG WITH MORE RECENT MESONET OBS AND
HIGH-RESOLUTION MODEL OUTPUT ALL SUGGEST THAT SMALL CRAFT ADVISORY
/SCA/ CONDITIONS ARE ONGOING ACROSS THE TYPICALLY WINDY WATERS
AROUND MAUI COUNTY AND THE BIG ISLAND. THE SCA REMAINS POSTED
THROUGH 6 AM FRIDAY. HI-RES MODEL OUTPUT ALSO SUGGESTS THAT THE
ADVISORY MAY NEED TO BE EXTENDED FOR THESE WINDY AREAS THROUGH
FRIDAY AND POSSIBLY INTO THE WEEKEND. WILL SEE IF THE OVERNIGHT
ASCAT PASS PROVIDES ANY ADDITIONAL INFORMATION BEFORE MAKING A
DECISION ON THIS.

THE HILO...PAUWELA AND MOKAPU POINT BUOYS ALL SHOW SHORT PERIOD
SEAS OF 7-9 FEET DUE TO TRADE WIND SWELL. THIS SWELL SHOULD
DECREASE SLIGHTLY OVER THE NEXT COUPLE DAYS AS THE HIGH TO THE
NORTHEAST WEAKENS...THEN PICK BACK UP EARLY NEXT WEEK AS THE NEXT
HIGH BUILDS NORTH OF THE AREA. SMALL SWELLS FROM THE NORTHWEST AND
SOUTH ARE ALSO IN STORE THROUGH THE REST OF THIS WEEK AND INTO
THIS WEEKEND. SURF ALONG SOUTH FACING SHORES MAY INCREASE SUNDAY
AND MONDAY AS A SWELL FROM EAST OF NEW ZEALAND REACHES THE
ISLANDS.

&&

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

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...BEDAL

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office