Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/26/20

Area Forecast Discussion...CORRECTED

National Weather Service Honolulu HI

 434 PM HST Fri Dec 25 2020

.SYNOPSIS...
Trade winds will gradually strengthen over the area into Saturday
as a surface high pressure system passes north of the islands. A
stationary front now over Kauai and Oahu will maintain periods of
showery weather to these two islands into Saturday. Remnants of
the front will spill over to Maui County as the front falls apart
tonight and Saturday. Drier conditions are on tap for the smaller
islands starting Sunday. Also, trade winds will be weaker next
week, with southeast winds over the smaller islands. This mean the
vog from Halemaumau crater has a chance of spreading to the
smaller islands.

&&

.DISCUSSION...
There has been some, perhaps, dissipation of the band of clouds
with embedded showers draped across Kauai and Oahu in the past
couple of hours, resulting in somewhat less frequent passing showers
and a bit more sunshine, especially the lee side. Upper level
disturbances in the form of gravity waves noted on satellite imagery,
moving from north to south, is playing havoc on this band, causing
to band to briefly dissipate then flare up again. Overall, clouds
and more frequent showers are likely to fill in after the sun sets.

The band of clouds is part of a stationary front that is forecast
to fall apart between tonight and Saturday. The southern fringe of
this band is about to advance onto Molokai this hour, so the forecast
for the clouds and showers to ease into Maui County tonight and
Saturday looks good. Moderate to strong trade winds now over Kauai,
is on the verge of reaching Oahu. Although surface winds are light
to moderate on Oahu, mountain waves noted on satellite imagery over
the lee of the Koolau Mountains is a sign of stronger winds above the
surface. Wind sensors across parts of Maui County and the Big
Island have seen an increase in trades already.

Aside for some small isolated pockets of afternoon clouds on
Maui, the Kona districts and Kau slopes on the Big Island, has
been sunny and dry for these the rest of Maui County and the Big
Island. As described above, increasing clouds and showers will
likely occur across the rest of Maui County in the coming hours.
And noted in the previous discussion, the front will not reach the
Big Island, but the models are hinting at an uptick in trade
showers Saturday night into Sunday.

Sunday also mark the beginning into a change in the weather pattern,
that calls for weakening trades, and trades turning southeast over
Kauai initially, then spread east to Maui by Monday. Light and
variable winds settles over the islands downwind of Maui and the
Big Island by Monday night. This wind pattern then holds to until
Tuesday or Wednesday, followed by breezy trade winds by New Year`s
Day.

&&

.AVIATION...
A showery cloud band associated with a nearly stationary front
extends across Kauai/Oahu and will continue to bring frequent MVFR
conditions, particularly across windward sections. An AIRMET for
mountain obscuration remains in effect. Conditions are expected to
improve somewhat this afternoon, before filling in again tonight
as the front slowly dissipates in place. However, MVFR ceilings
and occasional MVFR visibilities in showers will continue for
windward sections of Kauai/Oahu. Conditions will be primarily VFR
elsewhere across the state.

The Kauai VWP shows a layer of 25 knots of wind generally 3-5kft.
There is only a weak/elevated inversion so widespread turbulence
is not expected; however, with the strong winds and rough terrain
we could see some moderate turb. Currently, AMDAR flights out of
HNL and the Molokai VWP show winds only 15 kt still, so the AIRMET
for low-level turbulence was only issued for Kauai. Winds are
expected to increase elsewhere across the state by tonight, and
the AIRMET will likely be expanded.

&&

.MARINE...
The combination of strong tradewinds and elevated seas, from a fading
northwest swell, will necessitate the continuation of the Small Craft
Advisories for many coastal waters zones through at least Saturday.

The latest northwest swell will slowly trend down through the weekend
with a slight reinforcing bump Sunday night. The next significant
northwest swell may arrive Monday night or Tuesday morning and
bring advisory level surf. An even larger west-northwest swell may
fill behind that Tuesday night into Wednesday, which will likely
push surf heights to warning levels.

East facing shores will see an rise in choppy surf due to
strengthening and expanding area of strong tradewinds, generating
short period east- northeast swell through much of the weekend.
Surf along exposed east facing shore may approach advisory levels
by tomorrow evening and early Sunday, before subsiding through
midweek next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Saturday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters-
Alenuihaha Channel-Big Island Windward Waters.

Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay-
Pailolo Channel-Big Island Southeast Waters.


&&

$$


H Lau/Bravender/Almanza