High Wind in Hawaii, March 18, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
852 PM HST Tue Mar 17 2020

.SYNOPSIS...
A wet and unsettled weather pattern will continue across the
Hawaiian Islands through Wednesday as a kona low remains
stationary several hundred miles west of Kauai. The main threat
to the islands will come from heavy rain and flooding over already
saturated ground. The potential for severe weather continues
tonight and Wednesday across the western half of the state. The
kona storm will slowly weaken and drift northward on Thursday and
Friday, stabilizing the atmosphere, and reducing rainfall coverage
from east to west. Trade winds will fill in over the state as the
low retreats northward with more typical trade wind weather
forecast from Saturday through next week Tuesday.

&&

.DISCUSSION...
A kona storm located roughly 600 miles west of Kauai will continue
to produce periods of heavy showers and isolated thunderstorms
across the state for the next few days. A deep tropical moisture
plume with frequent heavy showers and isolated thunderstorms has
shifted over the eastern Hawaiian Islands tonight. The entire
state remains in a Flash Flood Watch through Wednesday Afternoon.
Satellite imagery shows another deep convective band might be
forming just west of Kauai as another upper trough moves into the
western half of the state. This means continued southeast to
southerly winds with another round of frequent showers, heavy at
times, potential for flash flooding, and thunderstorms development
through Wednesday across the western islands of Kauai and Oahu as
the convective band over Maui and the Big Island diminishes. Some
of these storms may become severe through Wednesday over the
western half of the state and we will re-evaluate this threat for
a potential Severe Thunderstorm Watch in the future.

Thursday and Friday...Long range guidance continues to show this
kona storm weakening and drifting slowly northward during this
period. As the low departs northward the subtropical ridge will
build in over the islands allowing trade winds with drying trends
to spread from east to west across the state. Global models are
in fair agreement with this solution, however due to normal
uncertainties with the movement of these kona lows the
precipitation timing in the forecast may change a bit during this
time period.

Saturday through next Tuesday...High pressure north of the state
will lead to moderate to breezy trade winds in a more typical
weather pattern with shower activity focused over windward and
mountain areas favoring the overnight time periods through the
first half of next week.

&&

.AVIATION...
A rather potent low pressure system, centered west of Kauai, will
draw SHRA and +SHRA over all islands from the south southwest through
the remainder of the night. Instability aloft will help to
generate isolated/scattered TSRA. MVFR and IFR conditions are
likely due to low ceilings and decreased visibility associated
with this activity.

AIRMET SIERRA remains in effect for the entire islands of Oahu,
Maui, and the Big Island above 1500 feet due to clouds and heavy
showers.

AIRMET TANGO is in effect for moderate turbulence aloft between FL180
to FL350 for the entire area. This will likely diminish through
tonight as this system slowly begins to weaken and move away from
the state by midweek.

AIRMET Zulu for moderate rime icing has been issued from Oahu to
the Big Island between FL180 and FL300.

&&

.MARINE...
Southeast winds are forecast to continue as the kona low to the
west begins to inch northward through the second half of the week.
Although wind speeds will remain in the fresh to strong category
over exposed waters, especially near the coasts where terrain-
induced accelerations occur with southeast flow (such as the
Hamakua coast and waters around South Point), light and variable
winds will remain possible over other areas (Oahu and Maui County
leeward waters). The largest seas are hovering around the advisory
level of 10 ft over the Kauai waters (recent altimeter pass
showed 10 ft near the south coast of Kauai). In addition to the
winds and seas, widespread heavy rainfall and thunderstorms will
continue.

Surf along north and west facing shores will remain small through
Thursday, then trend up late Thursday night through the day Friday
as a long-period, northwest swell builds down the island chain.
Latest satellite data showed storm-force westerly winds and seas in
the 30 to 36 ft range focused at the local area out of the 300 to
320 range (2000 to 2500 nm away from Hawaii) over the past 12-24
hrs. Although confidence remains low given the quick north-northeast
track, heights will near advisory levels for exposed north and west
facing shores at it peaks late Friday into Saturday. This swell
will hold Saturday, then slowly ease Sunday into early next week.

Surf along south facing shores will potentially remain up through
midweek for coasts exposed to southeast winds (Kauai/Oahu/SE Big
Island). Largest will remain along south facing shores of Kauai
through midweek, likely near or just shy of the 8 ft advisory level.
Otherwise, mainly small background south swells are anticipated
through the second half of the week. For the long-term, although
confidence remains low, guidance continues to show a 7-10 ft at 14-
15 second south-southwest swell impacting Pago Pago, Samoa Thursday-
Friday from recent Tropical Cyclone Gretel passing far to their
south-southwest. If this materializes, a decent sized, long-period
south-southwest swell will become a possibility for Hawaii by next
Monday (around the 23rd). Heights could near if not reach advisory
levels locally come Tuesday. More details will follow once this
source moves through Pago Pago.

Surf along east facing shores exposed to southeast winds will remain
rough through midweek. This will especially be the case for Kauai,
where heights will remain near the advisory level of 8 ft. Surf may
remain up through the second half of the week for all east facing
shores as a small trade wind swell fills in. Surf will ramp up early
next week as fresh to strong trades fill in locally and upstream.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Wednesday afternoon for all Hawaiian
Islands.

Winter Weather Advisory until 6 PM HST Wednesday for Big Island
Summits.

Small Craft Advisory until 6 PM HST Wednesday for Kauai
Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Oahu
Windward Waters-Kaiwi Channel-Maui County Windward Waters-
Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward
Waters-Big Island Southeast Waters.

&&

DISCUSSION...Bohlin
AVIATION...JT
MARINE...Gibbs

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HONOLULU HI
939 PM HST TUE MAR 17 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0930 PM     HEAVY RAIN       1 SSE NAHIKU            20.81N 156.09W
03/17/2020  U0.00 INCH       MAUI               HI   DEPT OF HIGHWAYS

            BOTH LANES OF THE HANA HIGHWAY ARE BLOCKED NEAR MILE
            MARKER 26 DUE TO A DOWNED TREE

&&

BIRCHARD

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HONOLULU HI
1143 PM HST TUE MAR 17 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1110 PM     FLASH FLOOD      KAWA FLATS              19.12N 155.53W
03/17/2020                   HAWAII             HI   LAW ENFORCEMENT

            HAWAII COUNTY POLICE DEPARTMENT REPORTS THE CLOSURE OF
            HIGHWAY 11 BETWEEN MILE MARKERS 58 AND 62 DUE TO WATER
            COVERING THE ROADWAY

&&

BIRCHARD