300
FXHW60 PHFO 080109
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
309 PM HST FRI AUG 7 2026
SYNOPSIS
MODERATE TO BREEZY STABLE TRADE WINDS WILL CONTINUE TODAY THROUGH
TOMORROW AFTERNOON WITH LIGHT SHOWERS EXPECTED OVER MOSTLY
WINDWARD AND MOUNTAIN AREAS. A PLUME OF TROPICAL MOISTURE IS THEN
FORECAST TO INCREASE RAIN CHANCES OVER THE BIG ISLAND AND TO A
LESSER EXTENT, THE REST OF THE ISLANDS LATE SATURDAY THROUGH
MONDAY. DRIER TRADE WINDS SHOULD THEN RETURN FROM TUESDAY THROUGH
THE END OF NEXT WEEK.
DISCUSSION
HIGH PRESSURE TO OUR NORTH WILL DRIVE MODERATE TO BREEZY TRADE
WINDS THROUGH MUCH OF NEXT WEEK. AN UPPER LEVEL RIDGE IS CURRENTLY
MOVING OVERHEAD TODAY ALONG WITH DRIER AIR, ALLOWING SHOWERS TO
STAY LIGHT AND ISOLATED MOSTLY TO WINDWARD AND MOUNTAIN AREAS.
THIS DRY SUMMERTIME PATTERN IS EXPECTED TO PERSIST THROUGH
TOMORROW AFTERNOON WITH CIMSS MIMIC PRECIPITABLE WATER VALUES
ESTIMATED AT AROUND 1.2-1.3 INCHES. THE 12Z BALLOON LAUNCH FROM
LAST NIGHT SHOWED PRECIPITABLE WATER VALUES AROUND 1.3 INCHES AS
WELL.
CURRENT SATELLITE IMAGERY DEPICTS A WEAK TROPICAL LOW WITH AN
ASSOCIATED TROPICAL WAVE APPROXIMATELY 560 NM EAST- SOUTHEAST OF
HILO. MODEL GUIDANCE PROJECTS THIS LOW TO WEAKEN INTO A TROUGH AS
IT MOVES WEST- NORTHWEST. THIS TROUGH WILL HAVE A DECENT MOISTURE
PROFILE ASSOCIATED WITH IT WHEN IT ARRIVES. CURRENT CIMSS MIMIC
PRECIPITABLE WATER SHOWS VALUES OF AROUND 1.8 TO 2 INCHES
ASSOCIATED WITH IT AND IT IS EXPECTED TO REACH THE BIG ISLAND BY
SATURDAY EVENING. RAINFALL CHANCES AND HUMIDITY WILL INCREASE FOR
THE BIG ISLAND AND MAUI COUNTY, THEN TO A LESSER EXTEND, OAHU AND
KAUAI SUNDAY INTO MONDAY. THE MOST RECENT GFS MODEL TIME- HEIGHT
CROSS SECTION DEPICTS THE BOUNDARY LAYER INVERSION WEAKENING, AS
CONDITIONS BECOME MORE UNSTABLE, AND MOISTURE DEEPENING UP TO AT
LEAST 15,000 FEET. THUS, FROM SATURDAY AFTERNOON THROUGH MONDAY,
EMBEDDED HEAVY RAINFALL WILL BE POSSIBLE FOR THE BIG ISLAND AND
MAUI COUNTY, ESPECIALLY FOR WINDWARD LOCATIONS.
THOUGH IT IS STILL TOO EARLY TO FINE TUNE THE FORECAST STORM
TOTAL AMOUNTS, TYPICALLY WETTER WINDWARD LOCATIONS ON MAUI AND THE
BIG ISLAND COULD PICK UP A COUPLE INCHES OF RAINFALL
ACCUMULATION. SUFFICIENT INSTABILITY MAY EXIST FOR A RUMBLE OF
THUNDER SUNDAY AFTERNOON OVER THE SOUTH OR SOUTHWEST SLOPES OF
MAUNA LOA ON THE BIG ISLAND, BUT CONFIDENCE IS TOO LOW AT THIS
TIME TO ADD TO THE CURRENT FORECAST PACKAGE.
TYPICAL SUMMERTIME STABLE TRADE WIND WEATHER WILL RETURN TUESDAY
THROUGH THE END OF THE WEEK WITH SCATTERED SHOWERS MAINLY WINDWARD
AND MAUKA AREAS DURING THE NIGHTS AND EARLY MORNINGS.
LOOKING INTO THE LONG RANGE FORECAST FOR LATE NEXT WEEK, BOTH
GOOGLE DEEPMIND AND GLOBAL DYNAMIC MODELS ARE SHOWING POTENTIAL
TROPICAL CYCLONE DEVELOPMENT IN THE CENTRAL PACIFIC. DETAILS ARE
FAR TOO EARLY AT THIS TIME BUT WARRANTS FURTHER MONITORING.
AVIATION
TRADE WINDS ARE FORECAST TO INCREASE THROUGH TOMORROW AS A
SURFACE HIGH PRESSURE SYSTEM TO OUR NORTHEAST STRENGTHENS AND
MOVES SLIGHTLY CLOSER TO HAWAII. A MOIST BAND IS MOVING WESTWARD
ACROSS MAUI COUNTY THIS AFTERNOON, AND IS EXPECTED TO BECOME MORE
DIFFUSE (SHOWERS WILL DECREASE) AS IT HEADS TOWARD OAHU THIS
EVENING. LEEWARD TURBULENCE WILL INCREASE TONIGHT INTO SATURDAY,
SO AN AIRMET TANGO MAY BECOME NECESSARY. LONG RANGE FORECAST CALLS
FOR CONTINUED TRADES THROUGH THE NEXT SEVEN DAYS.
MARINE
MODERATE TRADES WILL CONTINUE TO STRENGTHEN TO FRESH TO LOCALLY
STRONG SPEEDS BY THIS EVENING AS SURFACE TROUGHING TO THE
NORTHEAST WEAKENS AND A TROUGH APPROACHING FROM THE SOUTHEAST
ENHANCES THE LOCAL PRESSURE GRADIENT. A SMALL CRAFT ADVISORY IS IN
EFFECT FOR LOCALLY STRONG TRADES ACROSS THE TYPICAL WINDY
CHANNELS AND WATERS AROUND MAUI COUNTY AND THE BIG ISLAND. FRESH
TO LOCALLY STRONG TRADES WILL PERSIST THROUGH AT LEAST THE
WEEKEND, WITH THE STRONGEST WINDS OVER THE SOUTHERN PORTION OF
HAWAIIAN COASTAL WATERS AS THE SURFACE TROUGH NEARS.
BACKGROUND MEDIUM- AND LONG-PERIOD ENERGY WILL CONTINUE TO
PRODUCE SMALL SURF ALONG SOUTH-FACING SHORES THROUGH TONIGHT. A
SERIES OF LARGER, MEDIUM- TO LONG-PERIOD SOUTH SWELLS WILL CAUSE
SURF TO TREND UPWARD ALONG SOUTH- AND WEST-FACING SHORES FROM THIS
WEEKEND INTO EARLY NEXT WEEK. A MODERATE, LONG-PERIOD SOUTH SWELL
WILL PEAK NEAR HIGH SURF ADVISORY THRESHOLDS BY MIDWEEK.
ALONG EAST-FACING SHORES, TRADE WIND SWELL WILL REMAIN SLIGHTLY
BELOW SEASONAL AVERAGES TODAY BEFORE BUILDING THIS WEEKEND IN
RESPONSE TO STRENGTHENING TRADES. SURF ALONG NORTH-FACING SHORES
WILL REMAIN FLAT TO TINY THROUGH THE PERIOD, THOUGH A SMALL,
MEDIUM-PERIOD NORTH SWELL COULD BRING A SLIGHT BUMP ON SUNDAY.
DUE TO A COMBINATION OF PEAK MONTHLY HIGH TIDES AND WATER LEVELS
RUNNING HIGHER THAN PREDICTED, MINOR COASTAL FLOODING IS POSSIBLE
AROUND THE DAILY PEAK TIDE DURING THE AFTERNOON HOURS LATE THIS
WEEKEND INTO EARLY NEXT WEEK ALONG VULNERABLE SHORELINE AREAS.
HFO WATCHES/WARNINGS/ADVISORIES
SMALL CRAFT ADVISORY UNTIL 6 PM HST SATURDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.
DISCUSSION...TSAMOUS
AVIATION...PARKER
MARINE...FARRIS
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