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375
FXHW60 PHFO 221330
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST FRI AUG 22 2014

.SYNOPSIS...
TRADE WINDS WILL CONTINUE WITH MINOR CHANGES IN SPEED INTO NEXT
WEEK. SHOWERS GENERALLY WILL BE LIGHT...AND LIMITED TO SLOPES OF THE
BIG ISLAND EACH AFTERNOON...AND WINDWARD SLOPES ACROSS THE STATE ALL
DAY. HOWEVER...SHOWERS MAY BE SLIGHTLY MORE ACTIVE FROM SUNDAY NIGHT
INTO MONDAY.

&&

.DISCUSSION...
ALTHOUGH SATELLITE MEASUREMENTS STILL DETECTED A BUBBLE OF MOIST AIR
AROUND AND WEST OF THE SMALLER ISLANDS...A DRIER AIR MASS WITH MORE
STABLE LOW CLOUDS MOVED IN FROM THE NORTHEAST. SUBSIDENCE FROM A
MID-LEVEL RIDGE EXPANDING OVER THE STATE FROM THE NORTHEAST ALSO
HELPED TO SUPPRESS SHOWER DEVELOPMENT. THE STABLE LOW CLOUDS MAY YET
PRODUCE A FEW SHOWERS WHEN FORCED UP WINDWARD SLOPES...BUT
ACCUMULATION SHOULD REMAIN ON THE LIGHT SIDE.

SOLUTIONS LARGELY AGREED THAT THE EXPANSION OF THE RIDGE ALOFT WILL
BE BRIEF...AND THAT BROAD...SHALLOW TROUGHING THEN WILL EXPAND OVER
THE STATE FROM THE SOUTHWEST INTO THE WEEKEND. THE RESULTING
REDUCTION IN SUBSIDENCE WILL TEND TO COUNTER A DECREASE IN
PRECIPITABLE WATER UPWIND...SO THE PRACTICAL CHANGE IN TRADE SHOWERS
LIKELY WILL BE...SUBTLE. THE SHALLOW TROUGH AND WEAK RIDGE THEN WILL
ALTERNATE EXPANDING OVER THE STATE AND RETREATING...RESULTING IN
LITTLE NET EFFECT LOCALLY.

FROM SUNDAY INTO MONDAY...GUIDANCE STILL AGREED THAT A MOISTER AIR
MASS MAY PASS OVER THE ISLANDS. HOWEVER...THE PHASE OF THE
ALTERNATING WEAK RIDGING AND WEAK TROUGHING ALOFT WILL DETERMINE
WHETHER SHOWERS CAN UTILIZE THE FULL POTENTIAL OF THIS PRECIPITABLE
WATER. AS IS TYPICAL DURING TRADE-WIND WEATHER...SOLUTIONS PROBABLY
EXAGGERATED THE AMPLITUDE OF THESE CHANGES.

BY AROUND THE MIDDLE OF NEXT WEEK...SOME MODELS PREDICTED A MORE
LONGER-LIVED MID-LEVEL TROUGH TO DEVELOP OVER THE STATE FROM EAST TO
WEST....OR FROM NORTHEAST TO SOUTHWEST. THIS DEVELOPMENT APPEARED
TO BE LINKED IN SOME WAY WITH THE UNUSUAL TROPICAL CYCLONE ACTIVITY
IN THE EAST PACIFIC...SO CONFIDENCE IN THIS OUTCOME WAS NOT HIGH.

OTHERWISE...GUIDANCE PREDICTED THE SUBTROPICAL RIDGE TO THE NORTH TO
REMAIN MOSTLY IN PLACE THROUGH THE FORECAST PERIOD...KEEPING THE
TRADE WINDS BLOWING OVER THE ISLANDS. SIMILARLY...PRECIPITATION WILL
FOCUS OVER SLOPES WHERE OROGRAPHIC FORCING IS STRONGEST.

&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL ACROSS THE STATE TODAY AND TONIGHT.
PASSING TRADE SHOWERS AND ISOLATED MVFR CEILINGS WILL AFFECT MAINLY
WINDWARD AREAS.

&&

.MARINE...
WINDS LIKELY WILL PERSIST JUST BELOW THE THRESHOLD FOR A SMALL CRAFT
ADVISORY IN TYPICALLY WINDY AREAS AROUND MAUI COUNTY AND THE BIG
ISLAND THROUGH THE REST OF THE WEEK.

A HIGH SURF ADVISORY IS IN EFFECT FOR MOST SOUTH-FACING SHORES
THROUGH THIS AFTERNOON FOR SURF PRODUCED BY A SOUTH SWELL. A SERIES
OF SMALLER SOUTH SWELLS WILL CONTINUE TO ARRIVE THROUGH EARLY NEXT
WEEK...BUT THEY SHOULD PRODUCE SURF BELOW ADVISORY LEVELS.
SHORT-PERIOD TRADE-WIND SWELL WILL CONTINUE ALONG EAST-FACING
SHORES. NO SIGNIFICANT NORTHWEST SWELL IS EXPECTED THROUGH THE
WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST THIS EVENING FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-OAHU SOUTH SHORE-WAIANAE COAST-MOLOKAI
LEEWARD-LANAI-KAHOOLAWE-MAUI LEEWARD WEST-MAUI CENTRAL VALLEY-
LEEWARD HALEAKALA-KONA-SOUTH BIG ISLAND-KOHALA.

&&

$$

DISCUSSION/MARINE...RYSHKO
AVIATION...JACOBSON






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