Heavy Rain in Hawaii, July 16 to 17, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
930 AM HST THU JUL 16 2015

.SYNOPSIS...
MODERATE TRADE WINDS WILL CONTINUE THROUGH SUNDAY. AN AREA OF
ENHANCED MOISTURE MOVING IN FROM THE EAST WILL KEEP PASSING SHOWERS
THROUGH THE NEXT COUPLE OF DAYS...ESPECIALLY OVER WINDWARD AND MAUKA
AREAS. SOME OF THE LARGER SHOWERS WILL REACH LEEWARD LOCATIONS AT
TIMES. A DRIER TRADE WIND WEATHER PATTERN WILL DEVELOP ON SATURDAY
AND SUNDAY. THE TRADE WINDS ARE EXPECTED TO WEAKEN EARLY NEXT WEEK
WITH POTENTIAL FOR SEA BREEZES TO BRING AFTERNOON SHOWERS OVER
LEEWARD AND INTERIOR AREAS.

&&

.DISCUSSION...
SFC HIGH PRESSURE CENTERED FAR NE OF THE MAIN HAWAIIAN ISLANDS IS
KEEPING A MODERATE TRADE WIND REGIME THIS MORNING...WHILE WEAK
RIDGING REMAINS ALOFT OVER THE AREA. DESPITE THIS RELATIVELY STABLE
SYNOPTIC SETUP...THERE IS POTENTIAL FOR SOME LATE MORNING
SHOWERS...ESPECIALLY OVER THE BIG ISLAND N KOHALA DISTRICT...MAUI
COUNTY AND WINDWARD OAHU AS AN AREA OF ENHANCED MOISTURE JUST E OF
THE ISLANDS IS CARRIED BY THE TRADES.

LATEST MODEL SOLUTIONS SHOW THE AFOREMENTIONED SFC HIGH GRADUALLY
MIGRATING E AND STALLING DURING THE NEXT COUPLE OF DAYS. PRESSURE
GRADIENTS ACROSS THE AREA SHOULD REMAIN TIGHT ENOUGH TO MAINTAIN
THE CURRENT MODERATE TRADES THROUGH FRI. THE MODELS ALSO INSIST IN
BRINGING A BAND OF DEEPER MOISTURE ALONG THE TRAILING EDGE OF THE
MOISTURE FIELD...WITH POTENTIAL FOR SHOWERS TO AFFECT WINDWARD AND
MAUKA AREAS TODAY AND THROUGH LATE FRI. SOME OF THE LARGER SHOWERS
WILL REACH LEEWARD LOCATIONS OF THE SMALLER ISLANDS AT TIMES. BRIEF
HEAVY DOWNPOURS ARE ALSO POSSIBLE.

THE TRADES ARE EXPECTED TO INCREASE SLIGHTLY DURING THE WEEKEND WITH
A DRIER AIRMASS FILTERING INTO THE AREA FROM THE E. THEN BY LATE
SUN...A DEVELOPING DEEP TROUGH OVER THE E PACIFIC WILL LIKELY
DISRUPT THE TRADES AS THE SFC HIGH IS DISPLACED FURTHER TO THE N OF
THE ISLANDS. HENCE...THE TRADES MAY QUICKLY DECREASE AND ALLOW FOR
PERIODS OF LIGHT/VARIABLE WINDS TO DEVELOP OVER LEEWARD AREAS OF
MOST OF THE ISLANDS BY EARLY NEXT WEEK. THIS WILL BRING POTENTIAL
FOR SEA AND LAND BREEZE PATTERNS TO RETURN...WITH CLOUDS AND SHOWERS
AFFECTING LEEWARD AND INTERIOR SECTIONS DURING THE AFTERNOON AND
EARLY EVENING HOURS.

&&

.AVIATION...
A BAND OF SHOWERS WHICH FLARED UP IN THE NORTHERN COASTAL WATERS OF
THE BIG ISLAND AND MAUI EARLY THIS MORNING CONTINUES TO MOVE
WEST...AND THE BULK OF THE SHOWERS AS OF 19Z ARE IN THE COASTAL
WATERS NORTH OF MOLOKAI AND OAHU. CLOUD TOPS CONTINUE TO WARM AND
ARE NOW GENERALLY BETWEEN 10 AND 15 THOUSAND FEET WITH ISOLATED TOPS
REACHING 20 THOUSAND FEET. EXPECT WINDWARD AREAS OF OAHU TO CARRY
MVFR TO ISOL IFR CONDITIONS INTO THE EARLY AFTERNOON. KAUAI CAN
EXPECT SHOWER ACTIVITY TO INCREASE IN THE NEXT FEW HOURS AS THE BAND
OF SHOWERS MOVES TO THE WEST.

AIRMET SIERRA FOR MTN OBSCURATION IS POSTED OVER NORTH THROUGH EAST
SLOPES ON OAHU AND WILL BE ISSUED OVER KAUAI AS NEEDED. CONDITIONS
OVER MAUI AND MOLOKAI WILL CONTINUALLY IMPROVE INTO THE AFTERNOON
AND CAN EXPECT MAINLY VFR WITH PASSING MVFR IN SHOWERS. BIG ISLAND
WILL SEE MAINLY VFR WITH PASSING MVFR IS SHOWERS ALONG WINDWARD
AREAS AND LEEWARD AREAS CAN EXPECT AFTERNOON CLOUD BUILD UPS WITH
CLEARING IN THE EVENING.

&&

.MARINE...
THE TRADES ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS
THROUGH FRIDAY BEFORE A BRIEF SURGE MAY PRODUCE ADVISORY CONDITIONS
IN THE TYPICALLY WINDIER WATERS AROUND THE BIG ISLAND AND MAUI
COUNTY ON SATURDAY. A GRADUAL DECREASE IN TRADES IS EXPECTED TO
START LATER ON SUNDAY.

SMALL WEST AND SOUTHWEST SWELLS WILL PERSIST INTO EARLY NEXT WEEK...
WITH EASTERLY SWELL INCREASING FROM MULTIPLE SOURCES DURING THE
WEEKEND. SMALL...LONG PERIOD SWELLS FROM NORTHEAST PACIFIC TROPICAL
CYCLONES ENRIQUE AND DOLORES WILL LIKELY ARRIVE ON SATURDAY AND
EARLY MONDAY...RESPECTIVELY...AND WILL PERSIST INTO THE MIDDLE OF
NEXT WEEK. ALSO...A SHORT-PERIOD NORTHEAST SWELL IS ALSO FORECAST TO
OCCUR DURING THIS SAME TIME. THE COMBINATION OF THESE SWELLS MAY
CAUSE SURF TO BUILD...AND POSSIBLY APPROACH THE HIGH SURF ADVISORY
CRITERIA ALONG EAST FACING SHORES EARLY NEXT WEEK. FOR MORE
DETAILS...PLEASE SEE THE COLLABORATIVE NEARSHORE SWELL AND WIND
FORECAST /SRDHFO/ FOR MORE DETAILS.

&&

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

&&

DISCUSSION/MARINE...REYNES
AVIATION...EATON