Gale Warning 309, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
415 PM AKDT WED OCT 7 2015

.SHORT TERM...A LOW SOUTH OF THE GULF IS MAKING SLOW PROGRESS TO
THE NORTH AND IS HEADED FOR THE SOUTHWEST GULF. THE CIRCULATION
ABOUT THIS LOW IS LARGE...SO MUCH SO THAT THE ENTIRE EASTERN HALF
OF THE GULF WILL BE UNDER PREVAILING SOUTHERLY OR SOUTHEASTERLY
WINDS. IN ADVANCE OF THE FRONT, WINDS OVER THE GULF WILL REACH
GALE FORCE OUT OF THE SOUTHEAST TONIGHT WITH UP TO 40 KTS OVER
CLARENCE STRAIT FOR TOMORROW. ON THE INSIDE, HAVE KEPT WINDS
NORTHERLY OR EASTERLY EXCEPT FOR CLARENCE STRAIT, SOUTHERN CHATHAM
STRAIT, AND THE EASTERN PORTION OF FREDERICK SOUND. BY TOMORROW
MORNING, THE FRONT SHOULD BE PRODUCING STRONG WIND GUSTS ALONG
THE SOUTHERN OUTER COAST AND SOUTHERN INNER CHANNELS. EXPECT THOSE
WINDS TO PERSIST FOR MUCH OF THE DAY.

CONVECTIVE ENVIRONMENT BEHIND THE FRONT IS PRODUCING
THUNDERSTORMS AND LIGHTNING HAS BEEN DETECTED WEST OF HAIDA GWAII
FOR MUCH OF THE MORNING. INSTABILITY NEAR THE SURFACE AND ALOFT
SHOULD WEAKEN AS THE FRONT CONTINUES NORTH, SO NO MENTION OF
THUNDERSTORMS IN THE AFTERNOON FORECASTS. BLENDED TWP IMAGERY
INDICATING BETWEEN 1.5 AND 2.0 INCHES PRECIPITABLE WATER AND WATER
VAPOR IMAGERY SUGGESTS THIS FIRST ROUND OF PRECIPITATION IS
RELATED TO HURRICANE OHO. HAVE HEAVY PRECIP IN THE FORECAST FOR
TONIGHT AND TOMORROW...SPREADING NORTH WITH THE MAIN FRONTAL BAND,
BUT THE HEAVIEST PRECIP WILL OCCUR IN THE EXTENDED RANGE FORECAST
PERIOD. FOR DETAILS, SEE BELOW. AFTER A WEEK OF BASICALLY DRY
WEATHER, RIVERS AND STREAMS ARE DOWN AND THE SURFACE LAYERS ARE A
LITTLE MORE DRY, SO THERE WILL BE PLENTY OF ROOM FOR MOST, IF NOT
ALL OF THE RAINFALL TO INFILTRATE DOWN OR BE CARRIED AWAY BY
RIVERS WITHOUT FLOODING CONCERNS. MORE RAIN IS ON THE WAY IN THE
EXTENDED RANGE, SO HYDROLOGY WILL BECOME A CONCERN LATER ON THIS
WEEK.

USED NAM FOR UPDATES TO PRESSURE AND WIND. POP AND QPF FROM HIGH
AND LOW RESOLUTION NAM WITH A LITTLE HELP FROM GFS. TEMPS ADJUSTED
PER GFS MOS. OVERALL FORECAST CONFIDENCE IS AVERAGE.

.LONG TERM...ALL THE ATTENTION IS ON WHAT HAPPENS TO HURRICANE
OHO...CURRENTLY WELL NE OF HAWAII. MODELS HAVE COME INTO BETTER
AGREEMENT THAT IT WILL TRANSITION TO A VERY STRONG EXTRATROPICAL
STORM THAT MOVES INTO THE E GULF FRI. 12Z GFS/ECMWF/GEM WERE ALL
SHOWING THIS SYSTEM IN THE 950-960 MB RANGE OVER THE E GULF. 12Z NAM
WAS SOMEWHAT WEAKER...BUT 18Z RUN CAME IN STRONGER AND CLOSER TO
THE OTHER MODELS. THIS HAS PROMPTED US TO ISSUE A HIGH WIND WATCH
FOR ZONES 27 AND 28 FOR FRI MORNING THRU EARLY EVENING. I AM
CONCERNED THAT THE TRACK COULD DRIFT A LITTLE FURTHER TO THE
W...WHICH WOULD INCREASE HIGH WIND THREAT TO ZONES 23 THRU 26 FRI
AFTERNOON AND EVENING. LATER SHIFTS CAN ADD IN OTHER ZONES AS
NEEDED...BUT THE STRONGEST WINDS ARE CURRENTLY EXPECTED ALONG THE
SOUTHERN OUTER COAST FRI AFTERNOON. KEPT SE GULF MARINE WINDS
LIMITED TO 60 KT TO START STRONG UPWARD TREND FROM PREVIOUS
FORECAST...BUT THIS SYSTEM HAS CHANCE TO BRING A PERIOD OF 65+ KT
WINDS ON E SIDE OF LOW TRACK.

RAIN WILL BE SIGNIFICANT WITH THIS SYSTEM AS WELL DUE TO ITS
TROPICAL ORIGINS. HOWEVER...CURRENT THINKING IS THAT STREAMS WILL
NOT REACH FLOOD LEVELS OR ARE MUDSLIDES EXPECTED DUE TO THE
GROUND NOT BEING FULLY SATURATED DURING THE EVENT. LATER SHIFTS
WILL NEED TO MONITOR THE RAINFALL FROM THE PRECEDING SYSTEMS
THOUGH AS IT WOULD NOT TAKE MUCH MORE RAIN FROM THEM PLUS THE
RAINFALL WITH THE FRI SYSTEM TO CAUSE LOCAL FLOODING OR MUDSLIDES.

FURTHER OUT...BASICALLY USES THE LATEST WPC FROM SAT NIGHT ONWARD.
THERE IS POTENTIAL FOR ANOTHER SIGNIFICANT STORM SUN NIGHT AND
MON...BUT MODELS DIFFER SOME ON TRACK AND INTENSITY.

&&

.AVIATION...REDUCTIONS IN VISIBILITY WILL BE A FACTOR FOR
TOMORROW, THOUGH THEY ARE NOT EXPECTED TO GO BELOW MVMC. 5000FT
WINDS UP TO 50 KTS SUGGESTING THAT WINDS SHEAR WILL BE AN ISSUE
FOR TOMORROW WITH THE WORST CONDITIONS OVER THE SOUTHERN HALF OF
THE PANHANDLE. STRONG WINDS AND WIND GUSTS WILL ALSO BE A FACTOR ON
TAKEOFF AND LANDING FOR ALL BUT THE HEAVY IRON ON THURSDAY. WIND
GUST AND WIND SHEAR CONDITIONS DETERIORATING AND BECOMING
DANGEROUS THROUGH FRIDAY NIGHT AS THE REMNANTS OF HURRICANE OHO
TRACK NORTH OVER THE FAR EASTERN GULF.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM THURSDAY MORNING THROUGH THURSDAY AFTERNOON FOR
     AKZ027-028.
         HIGH WIND WATCH FROM FRIDAY MORNING THROUGH FRIDAY EVENING FOR
     AKZ027-028.
MARINE...GALE WARNING FOR PKZ036-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011>013-021-022-031>035.

&&

FRITSCH/RWT

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