Flash Flood and Heavy Rain in Hawaii, September 5 to 6, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST SAT SEP 5 2015

.SYNOPSIS...
A MOIST AND UNSTABLE AIRMASS WILL KEEP THE CHANCES FOR LOCALLY HEAVY
SHOWERS AND POSSIBLE THUNDERSTORMS THIS AFTERNOON. SLIGHTLY DRIER
WEATHER IS EXPECTED FOR EARLY NEXT WEEK. WINDS WILL REMAIN LIGHT
WITH DAYTIME SEA BREEZES AND NIGHTTIME LAND BREEZES EXPECTED. FOR
THE MIDDLE OF NEXT WEEK...MUCH WILL DEPEND ON THE TRACK AND
INTENSITY OF HURRICANE JIMENA.

&&

.DISCUSSION...
A MOIST AND UNSTABLE AIRMASS LIES OVER THE WEST END OF THE STATE
WHILE A SLIGHTLY DRIER AND MORE STABLE AIRMASS LIES OVER THE BIG
ISLAND. THE PRESSURE GRADIENT REMAINS WEAK ACROSS THE AREA AS HIGH
PRESSURE REMAINS FAR TO THE NORTHEAST OF THE STATE WHILE HURRICANE
JIMENA CONTINUES TO SPIN EAST OF THE AREA. DAYTIME HEATING ALONG
WITH SEA BREEZE CONVERGENCE WILL LIKELY CAUSE CLOUDS AND SHOWERS TO
FORM OVER LAND AREAS THIS AFTERNOON. A FEW THUNDERSTORMS ARE ALSO
EXPECTED DUE TO THE UNSTABLE AIRMASS IN PLACE. WITH THE GROUND
ALREADY SATURATED FROM RECENT RAIN EVENTS...THE LIKELIHOOD OF FLASH
FLOODING IS INCREASED. THUS A FLASH FLOOD WATCH IS POSTED FOR OAHU
AND KAUAI.

A SLIGHTLY DRIER AIRMASS MAY WORK ITS WAY IN FROM THE EAST MONDAY
AND TUESDAY. THE BACKGROUND WIND FLOW WILL GENERALLY BE FROM THE
NORTHEAST BUT WILL BE LIGHT ENOUGH FOR LOCAL LAND AND SEA BREEZES
TO OCCUR. A FEW SHOWERS CAN BE EXPECTED ESPECIALLY DURING THE
AFTERNOON HOURS.

FOR THE MIDDLE OF NEXT WEEK MUCH WILL DEPEND ON THE TRACK AND
INTENSITY OF JIMENA. JIMENA IS EXPECTED TO TRACK NORTH-NORTHWEST FOR
THE NEXT COUPLE DAYS...THEN TAKE A TURN TOWARD THE WEST OR WEST
SOUTHWEST. THE CURRENT FORECAST HAS US REMAINING IN A RATHER LIGHT
WIND REGIME WITH A WETTER WEATHER PATTERN EXPECTED DUE TO INCREASE
MOISTURE FROM JIMENA. HOWEVER...IF JIMENA TRACKS CLOSER TO THE
ISLANDS WE COULD SEE MORE SIGNIFICANT IMPACTS. EVERYONE SHOULD
FOLLOW THE FORECAST CLOSELY FOR NEXT WEEK.

&&

.AVIATION...
AN UPPER TROUGH NW OF KAUAI WILL KEEP THE AIR MASS OVER THE STATE
UNSTABLE. SCATTERED SHOWERS AND THUNDERSTORMS WILL BE MAINLY
CONCENTRATED AROUND KAUAI AND AREAS SOUTHWEST OF OAHU AND MAUI
COUNTY. BUT THEY COULD POP UP ANYWHERE OVER THE ISLAND CHAIN AND
NEARBY WATERS. DIURNAL PROCESSES WILL LIKELY ALLOW MUCH OF THE
SHOWERS AND THUNDERSTORMS...ESPECIALLY ANY THAT FORM OVER LAND...TO
DISSIPATE AFTER SUNDOWN. MAY SEE SOME MOUNTAIN OBSCURATIONS
WARRANTING AN AIRMET LATER TODAY.

&&

.MARINE...
A LARGE EAST SWELL FROM HURRICANE JIMENA WILL KEEP SURF AT WARNING
LEVELS FOR THE NEXT SEVERAL DAYS ALONG EAST FACING SHORES. THE
CURRENT ADVISORY LEVEL SOUTH SWELL WILL LINGER THROUGH MONDAY BEFORE
DIMINISHING TUESDAY AND WEDNESDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH UNTIL 6 PM HST THIS EVENING FOR NIIHAU-KAUAI-
OAHU.

HIGH SURF ADVISORY UNTIL 6 PM HST MONDAY FOR NIIHAU-KAUAI
LEEWARD-OAHU SOUTH SHORE-WAIANAE COAST-LANAI MAKAI-KAHOOLAWE-
MAUI LEEWARD WEST-LEEWARD HALEAKALA-KONA.

HIGH SURF WARNING UNTIL 6 PM HST MONDAY FOR KAUAI WINDWARD-OAHU
KOOLAU-OLOMANA-MOLOKAI-MAUI WINDWARD WEST-MAUI CENTRAL VALLEY-
WINDWARD HALEAKALA-SOUTH BIG ISLAND-BIG ISLAND NORTH AND EAST.

SMALL CRAFT ADVISORY UNTIL 6 PM HST MONDAY FOR ALL HAWAIIAN
WATERS EXCEPT MAALAEA BAY-

&&

SYNOPSIS/DISCUSSION/MARINE...BURKE
AVIATION...FUJII