Small Craft Advisory 18, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
907 PM HST MON APR 4 2016

.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE NORTHWEST TONIGHT...THEN MOVE
THROUGH THE ISLAND CHAIN TUESDAY AND TUESDAY NIGHT BEFORE STALLING
OUT NEAR THE BIG ISLAND BY EARLY WEDNESDAY. SHOWERS WILL INCREASE
ACROSS THE AREA ALONG AND AHEAD OF THE FRONT...WITH SOME LOCALLY
HEAVY RAINFALL POSSIBLE TONIGHT AND TUESDAY. RATHER WET CONDITIONS
ARE EXPECTED FOR WINDWARD AND MAUKA AREAS THROUGH MUCH OF THE WEEK
AS THE REMNANT MOISTURE ASSOCIATED WITH THE STALLED OUT FRONT REMAINS
ANCHORED IN PLACE OVER THE ISLAND CHAIN. BREEZY NORTH WINDS WILL
BUILD IN BEHIND THE FRONT TUESDAY AFTERNOON AND CONTINUE THROUGH
THURSDAY WHILE SHIFTING AROUND TO A MORE TYPICAL TRADE DIRECTION.
THE TRADES WILL WEAKEN BRIEFLY LATE IN THE WEEK AS ANOTHER COLD
FRONT PASSES BY TO THE NORTH OF THE ISLANDS...WITH HIGH PRESSURE
BUILDING NORTH OF THE STATE THEN RE-STRENGTHENING THE TRADE FLOW
OVER THE UPCOMING WEEKEND.

&&

.DISCUSSION...
CURRENTLY AT THE SURFACE...A COLD FRONT IS LOCATED AROUND 320
MILES NORTHWEST OF KAUAI. FURTHER UPSTREAM...A BROAD 1029 MB HIGH
IS LOCATED AROUND 1650 MILES NORTHWEST OF KAUAI. INFRARED
SATELLITE IMAGERY SHOWS MOSTLY CLOUDY SKIES ACROSS KAUAI AND
OAHU...WITH PARTLY CLOUDY SKIES IN PLACE ACROSS THE MAUI COUNTY
AND THE BIG ISLAND. MEANWHILE...RADAR IMAGERY SHOWS SHOWERS
SCATTERED ACROSS THE AREA...WITH THE MAIN CONCENTRATION IN THE
AREA OF ENHANCED CLOUD COVER IN THE VICINITY OF OAHU AND KAUAI.
MAIN SHORT TERM CONCERN FOR TONIGHT REVOLVES AROUND RAIN CHANCES.

REST OF TONIGHT...
THE COLD FRONT WILL CONTINUE TO MAKE STEADY PROGRESS SOUTHEASTWARD
TOWARD THE ISLAND CHAIN...REACHING THE NEARSHORE COASTAL WATERS
JUST NORTHWEST OF KAUAI BY 8 AM TUESDAY. DEEP LAYER MOISTURE WILL
INCREASE THROUGH THE NIGHT ACROSS THE WESTERN ISLANDS IN ADVANCE
OF THE FRONT. WHEN COMBINED WITH LARGE SCALE FORCING FOR ASCENT
PROVIDED BY A STRONG UPPER LEVEL TROUGH AND THE RIGHT REAR QUAD OF
A 160+ KNOT UPPER LEVEL JET...WE SHOULD SEE GOOD COVERAGE OF
SHOWERS BREAK OUT OVER KAUAI AND OAHU BY DAYBREAK TUESDAY...AND
SOME OF THE RAINFALL COULD BE LOCALLY HEAVY. ACROSS MAUI
COUNTY AND THE BIG ISLAND...ISOLATED TO SCATTERED SHOWERS WILL BE
POSSIBLE PRIOR TO DAYBREAK...PRIMARILY IN LEEWARD AREAS AND
SOUTH/SOUTHEAST FACING COASTLINES.

TUESDAY...
THE FRONT WILL PUSH THROUGH KAUAI TUESDAY MORNING AND THROUGH OAHU
TUESDAY AFTERNOON. SCATTERED TO NUMEROUS SHOWERS ARE EXPECTED
ALONG AND AHEAD OF THE FRONT...WITH BREEZY NORTHERLY WINDS
BUILDING IN BEHIND. HIGHEST RAIN CHANCES ARE EXPECTED ACROSS OAHU
AND KAUAI DURING THE MORNING HOURS...AND ACROSS OAHU AND MAUI
COUNTY DURING THE AFTERNOON HOURS. PLENTY OF LARGE SCALE FORCING
FOR ASCENT WILL REMAIN IN PLACE...SO SOME LOCALLY HEAVY RAINFALL
CAN/T BE RULED OUT.

TUESDAY NIGHT THROUGH THURSDAY NIGHT...
THE FRONT WILL PUSH THROUGH MAUI COUNTY TUESDAY NIGHT...THEN STALL
OUT AND DISSIPATE OVER THE BIG ISLAND ON WEDNESDAY. AT THE SAME
TIME...A STRONG RIDGE OF HIGH PRESSURE WILL TRACK EASTWARD AROUND
800-900 MILES NORTH OF THE STATE TUESDAY NIGHT THROUGH THURSDAY
NIGHT...KEEPING A BREEZY NORTH SHIFTING TO EAST-NORTHEAST TRADE
WIND FLOW IN PLACE ACROSS THE ISLAND CHAIN THROUGH THE PERIOD.
THERE WILL REMAIN SOME LARGE SCALE FORCING FOR ASCENT IN PLACE
ACROSS THE AREA AS WELL...WITH THE ISLANDS REMAINING WITHIN THE
RIGHT REAR QUAD OF A 100+ KNOT UPPER LEVEL JET. THIS IN
COMBINATION WITH THE REMNANT MOISTURE ASSOCIATED WITH THE FRONT
EXPANDING NORTHWARD OVER MAUI COUNTY WEDNESDAY NIGHT AND ACROSS
OAHU AND KAUAI THURSDAY AND THURSDAY NIGHT...ALONG WITH SOME WEAK
SURFACE TROUGHING DEVELOPING OVER THE ISLAND CHAIN...SHOULD KEEP
CONDITIONS UNSETTLED. SHOWERS ARE EXPECTED TO FAVOR WINDWARD AND
MAUKA LOCATIONS THROUGH THE PERIOD...BUT THE BREEZY TRADES WILL
LIKELY PUSH SOME SHOWERS INTO LEEWARD AREAS OF THE SMALLER ISLANDS
OCCASIONALLY AS WELL.

FRIDAY THROUGH NEXT MONDAY...
A COLD FRONT WILL APPROACH FROM THE NORTHWEST ON FRIDAY...THEN
STALL OUT NORTH OF THE ISLANDS SATURDAY AND SATURDAY NIGHT.
AS THE FRONT DISSIPATES AND ANOTHER RIDGE OF HIGH PRESSURE BUILDS
NORTH OF THE STATE SUNDAY THROUGH EARLY NEXT WEEK...WE EXPECT
THAT THE BREEZY TRADES WILL RETURN ONCE AGAIN. A CONVECTIVE
SHOWERY PATTERN IS EXPECTED ON FRIDAY AND SATURDAY WITH SHOWERS
FOCUSED PRIMARILY OVER LEEWARD AND INTERIOR AREAS OF THE ISLANDS.
THE RETURNING TRADES SHOULD FOCUS ACTIVITY BACK ACROSS WINDWARD AND
MAUKA LOCALES SUNDAY THROUGH EARLY NEXT WEEK.

&&

.AVIATION...
A COLD FRONT APPROACHING THE STATE FROM NORTHWEST WILL SPREAD CLOUDS
AND SCATTERED TO NUMEROUS SHOWERS ACROSS KAUAI LATE TONIGHT...OAHU
TUESDAY MORNING...AND MAUI COUNTY TUESDAY NIGHT. MVFR CEILINGS ARE
EXPECTED BEHIND THIS FEATURE. AN AIRMET FOR MTN OBSCURATION WILL
LIKELY BECOME NECESSARY ON KAUAI TUESDAY MORNING AND POSSIBLY ON
OAHU LATER IN THE DAY.

OTHERWISE...WEAK SOUTHEASTERLY FLOW WILL ALLOW LAND BREEZES TO
PREVAIL OVERNIGHT ACROSS LEEWARD PORTIONS OF MOST ISLANDS. WHILE
PATCHY CLOUDS AND ISOLATED SHOWERS WILL PERSIST ACROSS WINDWARD
COASTS AND SLOPES...SKIES OVER LEEWARD AREAS ARE EXPECTED TO
GRADUALLY CLEAR BY MORNING. LOW TOPPED CUMULUS BUILDUPS ARE EXPECTED
TO REDEVELOP ACROSS LEEWARDS PORTIONS OF MAUI AND THE BIG ISLAND ON
TUESDAY.

&&

.MARINE...
WINDS WILL CONTINUE TO WEAKEN AND SHIFT TO THE SOUTH AS HIGH
PRESSURE TRACKS EAST AND A COLD FRONT APPROACHES FROM THE WEST
TONIGHT INTO TUESDAY. THE FRONT WILL MOVE ACROSS THE SMALLER ISLANDS
THROUGH THE DAY TUESDAY THEN STALL NEAR THE BIG ISLAND ON WEDNESDAY
AND WEAKEN. STRONG NORTHERLY WINDS WILL FILL IN BEHIND THE FRONT
BEGINNING TUESDAY AFTERNOON...WHICH SHOULD PERSIST INTO THURSDAY
AS HIGH PRESSURE PASSES NORTH OF THE AREA. THE LATEST WAVE MODEL
GUIDANCE REMAINS IN GOOD AGREEMENT THROUGH THIS PERIOD AND DEPICTS
SEAS REACHING 10 FT ACROSS MOST EXPOSED WATERS BY WEDNESDAY AND
WEDNESDAY NIGHT. AS A RESULT...SMALL CRAFT ADVISORY CONDITIONS DUE
TO A COMBINATION OF WINDS AND SEAS ARE EXPECTED FOR ALL WATERS BY
WEDNESDAY...WHICH MAY PERSIST INTO THURSDAY. WINDS AND SEAS WILL
STEADILY TREND DOWN THURSDAY NIGHT THROUGH THE WEEKEND AS A WEAK
SURFACE TROUGH DEVELOPS OVER THE ISLANDS AND A WEAK FRONT
APPROACHES THE REGION FROM THE NORTHWEST.

ALTHOUGH THE SURF IS EXPECTED TO REMAIN BELOW ADVISORY LEVELS
THROUGH THE REMAINDER OF THE WEEK...ROUGH CONDITIONS DUE TO A
COMBINATION OF STRONG ONSHORE WINDS AND RISING SURF ARE EXPECTED
ALONG THE EXPOSED NORTH AND EAST FACING SHORES THROUGH THE MID-WEEK
PERIOD AS THE PREVIOUSLY DISCUSSED FRONTAL BOUNDARY MOVES THROUGH. A
MODERATE NORTHWEST SWELL IS ANTICIPATED OVER THE WEEKEND...WHICH
WILL LIKELY PERSIST THROUGH MONDAY BEFORE TRENDING DOWN. THIS SWELL
SHOULD REMAIN JUST BELOW ADVISORY LEVELS AS IT PEAKS THROUGH THE
DAY SUNDAY AND SUNDAY NIGHT.

&&

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

&&

DISCUSSION/MARINE...JELSEMA
AVIATION...BEDAL