Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 241406
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
406 AM HST Wed May 24 2017

.SYNOPSIS...
Strong trades will persist through today, pushing clouds and
showers across windward areas. Winds will gradually weaken through
the second half of the week, becoming light and variable through
the Memorial Day weekend. Daytime sea breezes and nighttime land
breezes will take over this weekend and bring warm and humid
weather with possible vog. A weak upper trough will pass over the
state this weekend and may provide some enhancement to afternoon
showers.

&&

.DISCUSSION...
Strong high pressure persists to our north, keeping trade winds
locally strong across the area this morning. Satellite loop shows
the area of showery low clouds which affected Oahu and Maui county
last night has moved west of the state. However, more clouds
embedded within trade flow are approaching Oahu and Kauai and may
reach these islands later this morning. Showery low clouds have
decreased dramatically across the Big Island, which nevertheless
retains its usual patchy trade wind shower swath across windward
slopes. The frontal cloud band just north of Kauai is rapidly
losing definition as it breaks up into large areas of broken to
overcast showery low clouds. Low clouds approaching Kauai from
the northeast may be one of these frontal band remnants.

Models show the trades will begin to weaken late tonight through
the end of the work week, then become quite light during the
holiday weekend. Background easterly flow will continue to tap
into lingering moisture over the state and fuel mainly windward
showers during the second half of the work week. Leeward areas
will see fewer showers during the night, but a hybrid sea breeze
pattern may produce afternoon cloud build ups and showers by
Friday. This weekend, background flow will likely veer to
southeasterlies, bringing voggy conditions to the smaller islands
through Memorial Day. Aloft, a weak upper level trough will swing
west to east over the islands and may enhance the afternoon sea
breeze driven showers.

&&

.AVIATION...
A strong surface high centered far north-northeast of Hawaii will
maintain the breezy low-level trade wind flow across the islands
today. Broken low clouds with embedded scattered showers will
continue to move slowly westward over the western islands this
morning. Expect additional low clouds and scattered trade showers
to persist into this afternoon, with periods of MVFR ceilings and
visibilities mainly over the higher terrain and along windward
facing slopes of most islands.

AIRMET Sierra remains in effect for mountain obscuration across
Oahu. This AIRMET may need to be expanded to include Kauai later
this morning.

The trade wind speeds are strong enough to generate turbulence
leeward of the mountains on all islands. Therefore, AIRMET Tango
remains in effect for low-level turbulence over and below 8
thousand feet downwind of the higher terrain.

&&

.MARINE...
The latest surface analysis showed a large area of high pressure
(1041 mb) encompassing much of the northern Pacific that was
centered around 1500 nm north-northeast of the waters. Remnants
of a lingering frontal boundary were analyzed from east to west
just north of the Kauai and Oahu waters. The pressure gradient
between this boundary and strong high pressure to its north
continues to support a large area of fresh to strong east-
northeast winds. Although the highest seas associated with these
winds are aiming at an area northwest of the local waters
(offshore NDBC buoys 51000 and 51101 peaked in the 9-11 ft range
today), seas across the windward waters have been coming in at the
exposed nearshore PacIOOS/CDIP buoys within 7 to 9 ft range
(highest Kauai/Oahu waters).

The latest model guidance has initialized well with the current
synoptic pattern discussed and depicts the strong winds locally and
north of the area holding through tonight, then trending down
through the second half of the week as high pressure shifts
northeast over the Gulf of Alaska and weakens. Land/sea breeze
conditions will become a possibility over the upcoming weekend,
which will allow the seas to trend down locally.

Surf along east facing shores will remain rough into Thursday due
to strong onshore winds, then trend down through the second half
of the week and into the weekend as the trades relax.

Surf along north facing shores will steadily trend down as the
northwest swell that peaked on Monday eases and shifts more out of
the north. For the long range, models are hinting at another
moderate north-northwest (340 deg) swell filling in early next
week due to a low tracking east of the Date Line over the weekend
and deepening as it passes well north of the state on Monday.

Surf along south facing shores is expected to trend down as the
small south swell eases. The largest south swell this season is
forecast to fill in late Thursday into Friday, peak Friday night
through Saturday night, then slowly ease into early next week.
This swell is currently impacting the Samoa buoy, where wave
heights were coming in slightly higher than predicted by guidance
earlier Tuesday (around one ft higher). A high surf advisory for
south facing shores will be likely late Friday through much of the
holiday weekend, before steadily easing into early next week.

In addition to the expected advisory-level surf through the Memorial
Day weekend along south facing shores, minor coastal flooding is
anticipated due to a combination of record level spring (king) tides
(especially for Maui County and Oahu) and large surf. Similar to the
April 28th through May 1st weekend, when the highest tides on record
were reported for Honolulu, impacts will include beach flooding and
standing water on roadways and low-lying areas near the coast
around the times of high tides each day through the weekend (see
listing of high tide times for Honolulu below).

High Tide times for Honolulu:

5/24 Wednesday  3:36 PM HST

5/25 Thursday   4:20 PM HST

5/26 Friday     5:07 PM HST (peak water levels/surf expected)

5/27 Saturday   5:55 PM HST (peak water levels/surf expected)

5/28 Sunday     6:46 PM HST

5/29 Monday     7:40 PM HST

For more detailed information on surf for Oahu, see the latest
Collaborative Nearshore Swell and Wind Forecast that was issued
Monday afternoon (www.prh.noaa.gov/hnl/pages/SRF.php#Discussion).

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION...Powell
AVIATION...Houston
MARINE...Gibbs


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