559  
FXHW60 PHFO 180654  
AFDHFO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HONOLULU HI  
854 PM HST FRI NOV 17 2017  
   
SYNOPSIS
 
 
LOW PRESSURE FAR TO THE NORTH OF THE ISLANDS WILL DROP SOUTH OVER  
THE NEXT COUPLE OF DAYS, DRAGGING A WEAK COLD FRONT SOUTHWARD  
THROUGH THE ISLANDS SATURDAY THROUGH SUNDAY. THE FRONT WILL BE  
ACCOMPANIED BY A BAND OF CLOUDS AND SHOWERS, WITH SHOWERS FAVORING  
NORTHERN SLOPES AND COASTS. AFTER THE FRONT COMES THROUGH, COOL  
NORTH AND NORTHWESTERLY WINDS ARE EXPECTED SATURDAY NIGHT THROUGH  
MONDAY. THE LOW TO OUR NORTH WILL MOVE AWAY FROM THE ISLANDS  
TUESDAY AND WEDNESDAY, AND TRADES WILL GRADUALLY RETURN. A LARGE,  
STRONG HIGH PRESSURE AREA TO OUR NORTH IS EXPECTED TO BRING BREEZY  
TO WINDY TRADES FOR THANKSGIVING DAY AND NEXT FRIDAY.  
 

 
   
DISCUSSION
 
 
CURRENTLY A STACKED AREA OF LOW PRESSURE, SURFACE AND ALOFT, IS  
LOCATED AROUND 950 MILES TO THE NORTH OF HONOLULU. MEANWHILE, A  
WEAK COLD FRONT IS LOCATED AROUND 250 MILES NORTH OF KAUAI.  
INFRARED SATELLITE IMAGERY SHOWS PARTLY TO MOSTLY CLOUDY SKIES  
ACROSS THE SMALLER ISLANDS, WHILE MOSTLY CLEAR CONDITIONS PREVAIL  
OVER THE BIG ISLAND. RADAR IMAGERY SHOWS SOME SCATTERED SHOWERS  
OVER WINDWARD AREAS OF THE SMALLER ISLANDS, WITH MAINLY RAIN FREE  
CONDITIONS IN LEEWARD LOCALES. MAIN SHORT TERM CONCERN REVOLVES  
AROUND RAIN CHANCES OVER THE NEXT FEW DAYS.  
 
TONIGHT THROUGH TUESDAY,  
THE STACKED LOW TO THE NORTH OF THE STATE WILL SLOW ITS  
PROGRESSION AS IT DROPS SOUTHWARD TONIGHT AND SATURDAY, THEN  
STALL AROUND 600 MILES TO THE NORTH-NORTHEAST OF HONOLULU SATURDAY  
NIGHT. THE STACKED LOW WILL THEN EDGE EASTWARD SUNDAY THROUGH  
MONDAY, BEFORE LIFTING NORTHEASTWARD AND AWAY FROM THE ISLAND  
CHAIN MONDAY NIGHT AND TUESDAY. A WEAK COLD FRONT WILL ALSO SHIFT  
SOUTHWARD THROUGH KAUAI AROUND NOON ON SATURDAY, THROUGH OAHU  
LATE SATURDAY AFTERNOON, MAUI COUNTY SATURDAY NIGHT AND THROUGH  
THE BIG ISLAND ON SUNDAY. LIGHT NORTHERLY WINDS WILL DEVELOP OVER  
KAUAI AND OAHU TONIGHT, WHILE LIGHT AND VARIABLE WINDS AND LAND  
BREEZES DOMINATE ACROSS MAUI COUNTY AND THE BIG ISLAND. THE  
NORTHERLY FLOW WILL INCREASE OVER THE WESTERN ISLANDS ON SATURDAY,  
WITH LIGHTER NORTHERLY WINDS ALLOWING FOR SEA BREEZES ACROSS MAUI  
COUNTY AND THE BIG ISLAND. THE NORTH-NORTHWESTERLY WINDS WILL  
THEN OVERSPREAD MAUI COUNTY SATURDAY NIGHT AND THE BIG ISLAND ON  
SUNDAY. LIGHT TO MODERATE NORTH-NORTHWESTERLY FLOW WILL CONTINUE  
SUNDAY NIGHT, SHIFT MORE NORTHERLY ON MONDAY, THEN SHIFT AROUND TO  
THE NORTHEAST ON TUESDAY.  
 
AS FOR SENSIBLE WEATHER DETAILS, SHOWERS WILL FAVOR NORTHERN  
SLOPES AND COASTS THROUGH THE PERIOD, WITH AN INCREASE IN SHOWERS  
EXPECTED IN ASSOCIATION WITH THE FRONT AS IT MOVES DOWN THE ISLAND  
CHAIN. SOME SHOWERS WILL SPILL INTO LEEWARD LOCATIONS FROM TIME TO  
TIME AS WELL, PARTICULARLY AS THE FRONT MOVES THROUGH. IN  
ADDITION, SOME AFTERNOON/EVENING SHOWER DEVELOPMENT WILL BE  
POSSIBLE IN LEEWARD AREAS OF MAUI COUNTY AND THE BIG ISLAND ON  
SATURDAY DUE TO SEA BREEZE ENHANCEMENT.  
 
FOLLOWING THE FRONTAL PASSAGE, COOLER WEATHER WILL PREVAIL, WITH  
SURFACE DEWPOINTS DROPPING INTO THE 50S IN MANY AREAS, MAKING IT  
FEEL VERY COMFORTABLE ACROSS THE ISLAND CHAIN.  
 
SUMMIT LEVEL WINDS CONTINUE TO BOUNCE BETWEEN ADVISORY AND WARNING  
LEVELS THIS EVENING, BUT THEY SHOULD INCREASE SOLIDLY BACK TO WARNING  
LEVELS LATER TONIGHT THROUGH SUNDAY AS THE UPPER LOW MOVES  
CLOSER. WINDS AT THE SUMMITS SHOULD THEN BEGIN TO TREND DOWN  
SUNDAY NIGHT AND MONDAY AS THE UPPER LOW BEGINS TO OPEN UP AND  
SHIFT EASTWARD AND AWAY FROM THE ISLAND CHAIN.  
 
TUESDAY NIGHT THROUGH NEXT FRIDAY,  
A STRONG AREA OF HIGH PRESSURE WILL BUILD EASTWARD WELL TO THE  
NORTH OF THE STATE, INCREASING THE GRADIENT ACROSS THE ISLANDS AND  
SHIFTING THE WINDS BACK INTO A MORE TYPICAL TRADE WIND DIRECTION.  
THE TRADES ARE EXPECTED TO INCREASE TO MODERATE LEVELS ON  
WEDNESDAY, WITH BREEZY TO WINDY CONDITIONS THEN EXPECTED FOR  
THANKSGIVING DAY AND FRIDAY. WITH THE RETURNING TRADES, A MORE  
TYPICAL WINDWARD AND MAUKA SHOWER PATTERN IS EXPECTED TO RESUME  
ACROSS THE ISLAND CHAIN.  
 

 
   
AVIATION
 
 
A CLOUD BAND ASSOCIATED WITH A WEAK COLD FRONT WILL MOVE INTO  
KAUAI AND OAHU FROM THE NORTH ON SATURDAY. EXPECT SCATTERED CLOUDS  
AND ENHANCED SHOWERS IN THE AFTERNOON ESPECIALLY OVER MOUNTAINS  
AND ALONG NORTHWEST THROUGH NORTHEAST SLOPES OF ALL ISLANDS.  
 
NO AIRMETS ARE IN EFFECT, AND NONE ARE EXPECTED OVERNIGHT.  
 

 
   
MARINE
 
 
WINDS HAVE TRENDED DOWN ACROSS THE WATERS AND WILL GRADUALLY SHIFT  
OUT OF THE NORTH OVERNIGHT INTO SATURDAY AS A FRONTAL BOUNDARY AND  
LOW PRESSURE DIVE SOUTHWARD ACROSS THE REGION. GUIDANCE SUPPORTS  
THIS MORE NORTHERLY FLOW HOLDING THROUGH THE WEEKEND AND INTO NEXT  
WEEK AS LOW PRESSURE ASSOCIATED WITH THIS FRONTAL BOUNDARY STALLS  
NORTH OF THE STATE. WINDS SHOULD REMAIN BELOW ADVISORY LEVELS  
THROUGH THE WEEKEND, BUT THE RATHER UNUSUAL WIND DIRECTIONS WILL  
RESULT IN DIFFERENT AREAS OF TERRAIN ACCELERATION, SUCH AS THROUGH  
THE KAULAKAHI CHANNEL ON SATURDAY AND SATURDAY NIGHT AND THE  
HAMAKUA COAST ON SUNDAY. MODERATE TRADES RETURN TUESDAY AND  
WEDNESDAY NEXT WEEK.  
 
SURF ALONG EAST FACING BEACHES WILL GRADUALLY TREND DOWN OVER THE  
WEEKEND AS THE TRADES RELAX AND THE FLOW SHIFTS OUT OF THE NORTH AS  
THE AFOREMENTIONED FRONT DROPS SOUTH INTO THE AREA AND SEAS CONTINUE  
TO LOWER.  
 
SURF ALONG NORTH FACING SHORES WILL REMAIN UP THROUGH MUCH OF THE  
PERIOD DUE TO OVERLAPPING NORTHERLY SWELLS MOVING THROUGH THE LOCAL  
WATERS. THE ANOMALOUS PATTERN ACROSS THE NORTHERN PACIFIC FEATURING  
STORMS DIVING SOUTHWARD ACROSS THE EASTERN PACIFIC FROM THE  
ALEUTIANS/GULF OF ALASKA TO NEAR THE ISLANDS DUE TO A BLOCKING  
RIDGE THAT REMAINS ESTABLISHED OVER THE CENTRAL PACIFIC IS  
PROJECTED TO CONTINUE THROUGH MUCH OF NEXT WEEK.  
 
THE LATEST ANALYSIS SHOWED A STRONG PRESSURE GRADIENT BETWEEN 1040  
MB HIGH PRESSURE CENTERED NEAR THE ALEUTIANS AROUND 45N AND 1010 MB  
LOW CENTERED DIVING SOUTHWARD ACROSS THE EASTERN PACIFIC SEVERAL  
HUNDRED NAUTICAL MILES NORTH OF THE ISLANDS. PERSISTENT STRONG- TO  
GALE-FORCE NORTHERLY FLOW LOCKED IN BETWEEN THESE TWO SYNOPTIC  
FEATURES FOCUSED TOWARD THE LOCAL AREA OVER THE PAST COUPLE OF  
DAYS WILL TRANSLATE TO THE NEXT LARGE NORTHERLY SWELL THROUGH THE  
SECOND HALF OF THE WEEKEND AND INTO THE UPCOMING WEEK. PROVIDED  
THE PROXIMITY OF THIS GENERATION SOURCE TO THE LOCAL AREA, NO  
SIGNIFICANT TIMING OR SWELL MAGNITUDE DIFFERENCES ARE DEPICTED  
BETWEEN THE ECMWF-WAVE AND WAVEWATCH III SOLUTIONS AS THIS SOURCE  
MOVES THROUGH THE ISLANDS.  
 
THE NORTH (350 DEG) SWELL WILL BEGIN TO FILL IN SATURDAY NIGHT, PEAK  
SUNDAY INTO MONDAY BEFORE TEMPORARILY TRENDING DOWN TUESDAY INTO  
WEDNESDAY. THE ECMWF SOLUTION IS A BIT MORE BULLISH WITH THE LOW  
DROPPING FARTHER SOUTH AND DEPICTS A SECONDARY PEAK LATE MONDAY  
THROUGH MONDAY NIGHT. THE OVERNIGHT PACKAGE WILL SUPPORT A BLEND  
OF THESE TWO SOLUTIONS TO EXPRESS UNCERTAINTY. SURF ALONG NORTH  
FACING SHORES WILL NEAR WARNING LEVELS AROUND THE PEAK SUNDAY,  
THEN LIKELY HOLD THROUGH MONDAY NIGHT ABOVE ADVISORY-LEVELS (15  
FT FACES) BEFORE EASING TUESDAY INTO WEDNESDAY.  
 
AS THE SWELL IS PEAKING ALONG NORTH FACING SHORES SUNDAY INTO  
MONDAY, THE PROGRESSIVE PATTERN ACROSS THE NORTHEAST PACIFIC IS  
PROJECTED TO CONTINUE AS ANOTHER GALE- TO STORM-FORCE LOW EMERGES  
OVER THE GULF OF ALASKA NEAR KODIAK ISLAND AND TRACKS SOUTH-  
SOUTHEASTWARD ACROSS THE NORTHEAST PACIFIC MONDAY THROUGH TUESDAY. A  
REINFORCING NORTHERLY SWELL ASSOCIATED WITH THIS SOURCE IS EXPECTED  
TO FILL IN BY WEDNESDAY NIGHT, LIKELY TRANSLATING TO SURF NEARING  
THE WARNING MARK ALONG NORTH FACING SHORES ONCE AGAIN BY THURSDAY.  
THIS SOURCE WILL HOLD THROUGH THE SECOND HALF OF THE WEEK BEFORE  
EASING INTO THE WEEKEND.  
 
SPECTRAL DENSITIES AT THE OFFSHORE BUOYS SOUTH OF THE ISLANDS ARE  
SHOWING SOME ENERGY OUT OF THE SOUTH-SOUTHWEST WITHIN THE 15 TO  
17 SEC BANDS. THIS IS FROM RECENT ACTIVITY ACROSS THE SOUTHERN  
PACIFIC NEAR NEW ZEALAND AND THE TASMAN SEA. SURF ALONG SOUTH  
FACING SHORES WILL REFLECT THIS AND LIKELY HOLD THROUGH THE  
WEEKEND AT SMALL LEVELS. SIMILAR SOURCES ARE EXPECTED INTO NEXT  
WEEK THAT WILL KEEP THE SURF FROM GOING FLAT ALONG SOUTHERN  
EXPOSURES.  
 
SEE THE LATEST COLLABORATIVE NEARSHORE AND SWELL FORECAST FOR OAHU  
FOR MORE DETAILS ON THE SURF AT: WWW.PRH.NOAA.GOV/HNL/PAGES/SRF.PHP  
 

 
   
HFO WATCHES/WARNINGS/ADVISORIES
 
 
HIGH WIND WARNING UNTIL 6 PM HST SUNDAY FOR BIG ISLAND SUMMITS.  
 

 
 

 
 
DISCUSSION...JELSEMA  
AVIATION...BOHLIN  
MARINE...GIBBS  
 
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