Flood Watch 3, NWS Honolulu, HI

396 
WGHW60 PHFO 220116
FFAHFO

Flood Watch
National Weather Service Honolulu HI
316 PM HST Tue Dec 21 2021

...FLASH FLOOD WATCH FOR THE BIG ISLAND THROUGH TONIGHT...

HIZ023-026-027-051>054-221530-
/O.CON.PHFO.FA.A.0003.000000T0000Z-211222T1600Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Kona-Kohala-Big Island Interior-Big Island South-Big Island
Southeast-Big Island East-Big Island North-
316 PM HST Tue Dec 21 2021

...FLOOD WATCH REMAINS IN EFFECT THROUGH LATE TONIGHT...

* WHAT...Flash flooding caused by excessive rainfall continues to be 
  possible.

* WHERE...The Big Island.

* WHEN...Through late tonight.

* IMPACTS...Flood prone roads and other low lying areas may be 
  closed due to elevated runoff and overflowing streams. Urban areas 
  may receive more significant flooding and property damage due to 
  rapid runoff.

* ADDITIONAL DETAILS...
  - Recent rainfall has produced nearly saturated conditions,
    especially over windward slopes of the Big Island. A passing
    upper disturbance is expected to produce additional heavy
    showers and thunderstorms that could lead to flash flooding
    through tonight. The highest flood risk will be across
    windward slopes, though heavy rainfall could effect the
    entire island.


PRECAUTIONARY/PREPAREDNESS ACTIONS...

You should monitor later forecasts and be prepared to take action 
should Flash Flood Warnings be issued.

&&

$$

WROE

559 
WGHW60 PHFO 221311
FFAHFO

URGENT - IMMEDIATE BROADCAST REQUESTED
Flood Watch
National Weather Service Honolulu HI
311 AM HST Wed Dec 22 2021

...FLASH FLOOD WATCH FOR THE BIG ISLAND THROUGH THIS AFTERNOON...

HIZ023-026-027-051>054-230315-
/O.EXT.PHFO.FA.A.0003.000000T0000Z-211223T0400Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Kona-Kohala-Big Island Interior-Big Island South-Big Island
Southeast-Big Island East-Big Island North-
311 AM HST Wed Dec 22 2021

...FLOOD WATCH NOW IN EFFECT THROUGH THIS AFTERNOON...

* WHAT...Flash flooding caused by excessive rainfall continues to be 
  possible.

* WHERE...The Big Island.

* WHEN...Through this afternoon.

* IMPACTS...Flood prone roads and other low lying areas may be 
  closed due to elevated runoff and overflowing streams. Urban areas 
  may receive more significant flooding and property damage due to 
  rapid runoff.

* ADDITIONAL DETAILS...
  - A passing upper-level disturbance will produce heavy showers
    and thunderstorms that could lead to flash flooding today.
    The highest flood risk will be across windward slopes, though
    heavy rainfall and thunderstorms could occur anywhere.


PRECAUTIONARY/PREPAREDNESS ACTIONS...

You should monitor later forecasts and be prepared to take action 
should Flash Flood Warnings be issued.

&&

$$

Birchard

534 
WGHW60 PHFO 230102
FFAHFO

Flood Watch
National Weather Service Honolulu HI
302 PM HST Wed Dec 22 2021

HIZ023-026-027-051>054-230215-
/O.CAN.PHFO.FA.A.0003.000000T0000Z-211223T0400Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Kona-Kohala-Big Island Interior-Big Island South-Big Island
Southeast-Big Island East-Big Island North-
302 PM HST Wed Dec 22 2021

...FLOOD WATCH IS CANCELLED...

The Flash Flood Watch is cancelled for the island of Hawaii in 
Hawaii County.

Although rain is expected to continue, particularly over the 
windward side of the island, flooding is no longer expected to pose 
a threat.

$$

M BALLARD

Area Forecast Discussion
National Weather Service Honolulu HI
953 AM HST Tue Dec 21 2021

.SYNOPSIS...
Breezy and rather wet and unstable trade wind weather will
persist today. Showers will favor windward and mauka areas and
will periodically be blown across leeward sections on the gusty
trades. Wet conditions and a chance of thunderstorms will continue
across the Big Island into Wednesday, while some drying occurs
from north to south across the rest of the island chain. Slightly
weaker trade winds and a typical pattern of mainly windward and
mauka showers is expected Thursday through Christmas. Winds may
shift southeasterly near Kauai Sunday or early next week.

&&

.DISCUSSION...
Breezy and rather wet and unstable trade wind weather will hold
for this first day of winter. A highly amplified pattern over the
Pacific is producing a strong 1038 mb surface high far north of
the state. The high is driving breezy and gusty trade winds and
has pushed a narrow band of diffuse low level moisture over the
islands. Meanwhile, the deep ridge aloft supporting the surface
high is being undercut by the west Pacific jet stream and an upper
level trough to the northeast of the state, leading to instability
that is enhancing local rainfall. As a result, frequent showers
will continue to affect windward areas of all islands today, while
showers periodically blow across leeward areas from Kauai to
Maui. A disturbance aloft is triggering thunderstorms just south
and west of the coastal waters, and as this feature creeps
eastward, expect some heavy showers and thunderstorms to flare
over and around the Big Island this afternoon.

Tonight and Wednesday, breezy trades will hold, but a decrease in
shower activity is expected across Kauai, Oahu, and Molokai as the
low level band of moisture pushes south. Wet and unsettled
conditions with heavy showers and thunderstorms will persist on
the Big Island, especially windward, as the upper disturbance
passes just south tonight and drifts off to the east on Wednesday.
At this time, we are not planning to issue a Flash Flood Watch
for the Big Island, though we will closely monitor the situation.
In addition, a Winter Weather Advisory for the high summits of the
Big Island will likely be issued later in the day.

Moderate to locally breezy trade winds and a somewhat typical
pattern of windward and mauka showers is expected for Thursday
through Christmas Day. The GFS and ECMWF models depict the band
of low level moisture moving just south of the islands. High
pressure will hold far north of the state and will maintain
moderate to locally breezy trade winds. Drier mid level air will
push down from the north, but the atmosphere will remain slightly
unstable as upper level troughing lingers overhead. Expect
rainfall to be focused over windward slopes of all islands. As
showers develop over leeward and interior Big Island each
afternoon, we cannot rule out a thunderstorm.

Sunday into early next week, deep low pressure will develop
several hundred miles northwest of the state. Winds will likely
shift southeasterly near Kauai, but even though there is some
uncertainty at this time, deep moisture and instability look to
remain west of Kauai.

&&

.AVIATION...
Easterly trade winds remain breezy through the forecast period,
favoring a continued tempo moderate turbulence over the lee of
the mountains. See AIRMET TANGO below. Otherwise, the persistent
trades will concentrate showers mainly along windward portions of
the islands, where CIGS and VSBYs could briefly drop to MVFR
especially over eastern sections of the Big Island.

A band of deeper layered moisture and instability will
lift up across the Big Island through tomorrow, increasing the
threat of thunderstorms southeast of Maui. Abundant mid-upper
level clouds will persist elsewhere over the island chain.

AIRMET SIERRA remains in effect for northeast thru east facing
mountain slopes above 2500 feet for Kauai, Oahu, Maui, Molokai,
and the Big Island due to clouds and showers.

AIRMET TANGO remains in effect for all islands over and
immediately south through west of mountains for tempo moderate
turbulence below 9000 feet.

&&

.MARINE...
A strong 1038 mb high is centered far north of the state. This is
providing for rather strong trade winds across the entire area. A
Small Craft Advisory (SCA) is currently posted for all Hawaiian
Coastal Waters due to these strong winds and associated seas.
These conditions are expected to continue over the next few days.
An unstable airmass in the island vicinity may allow for some
locally heavy showers a few thunderstorms to form over the coastal
waters through Wednesday mainly around the Big Island. Winds will
drop off a bit as we head into the weekend as the high to the
north weakens and an area of low pressure moves a bit closer to
the state from the west.

A High Surf Advisory (HSA) is currently in effect through
Wednesday for east facing shores as a moderate size north-
northeast swell moves across the area. North facing shores will
also experience surf heights just below HSA levels due to its
higher criteria. This swell will lower very slowly through Friday
with surf heights likely remaining at or just above HSA levels for
east facing shores. As we head into the weekend and on into early
next week, the trade wind swell will become the dominant feature
from a more easterly direction and a shorter period.

Swells from the west and northwest directions will be well below
seasonal levels for this time of year with just small pulses
expected through the remainder of the week and on into early next
week. South facing shores will remain small throughout the
forecast period with just background swell energy expected.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Wednesday for Olomana-Maui
Windward West-Kauai East-Koolau Windward-Molokai Windward-
Molokai Southeast-Windward Haleakala-Big Island East-Big Island
North.

Small Craft Advisory until 6 PM HST Thursday for all Hawaiian
waters.

&&

DISCUSSION...Wroe
AVIATION...SWR/JVC
MARINE...Burke