834 
FXHW60 PHFO 090641
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
841 PM HST Fri May 8 2020

.SYNOPSIS...
A trade wind weather pattern will continue through early next 
week, as high pressure slowly passes far north of the state. 
Clouds and passing showers will generally favor windward and 
mauka areas of Maui and the Big Island tonight, with the greatest
chances for showers shifting to windward Kauai during the weekend
and early next week. Winds will likely weaken Tuesday and may be 
disrupted with a sea breeze and land breeze pattern setting up
Wednesday through late next week.

&&

.DISCUSSION...
Currently at the surface, a 1026 mb high centered around 900 miles
northwest of Kauai, is driving moderate northeasterly trades
across the island chain this evening. Infrared satellite imagery
shows clear to partly cloudy skies from Kauai to Lanai, with 
partly to mostly cloudy conditions across Maui and the Big Island.
Radar imagery shows scattered showers moving into windward
sections of Maui and the Big Island, with an isolated shower or
two moving into windward Oahu and Kauai. Leeward showers on the
Big Island are beginning to fizzle out, with very little rainfall
in other leeward locales. Main short term concern revolves around
trade wind trends and rainfall chances through the weekend.

High pressure north of the state will build slowly eastward
through the weekend into early next week. Moderate northeasterly 
trades will transition over to a more typical east-northeasterly 
direction by Sunday and Monday, with only minor fluctuations in
strength expected. The trades will ease on Tuesday as a weak 
surface trough develops northwest of the islands, weakening the 
surface ridge north of the state. The gradient will ease further
Wednesday through Friday, as high pressure shifts into the east 
Pacific and a cold front approaches from the northwest. This will
likely bring a light wind pattern featuring daytime sea breezes
and overnight land breezes to the island chain.

As for weather details, a couple cloud bands in the vicinity of 
Maui and the Big Island, as well as Kauai, will bring a bit higher
shower activity to windward areas of these island through
Saturday morning, with drier conditions expected across Oahu 
where only a few windward showers are expected. The cloud/shower 
band near Kauai, is expected to hold through the afternoon 
Saturday, while the band over the eastern islands sags southward 
to mainly affect the Big Island. Showers will be most prevalent in
windward sections of Kauai and the Big Island, where some leeward
shower activity will likely also develop as a result of daytime 
heating. A few windward showers will be possible over Maui County 
and Oahu Saturday afternoon, but drier conditions are expected 
here. Very little change in the pattern is expected Saturday night
and Sunday, with the two areas of slightly higher moisture 
affecting Kauai and the Big Island, bringing more shower activity 
to these locales, while drier conditions prevail with mainly 
windward showers across Oahu and Maui County. 

The cloud band near the Big Island is expected to become more 
diffuse and Sunday night and Monday, allowing a more uniform 
scattered shower regime to develop across windward sections of 
Oahu eastward to the Big Island, with a few leeward showers 
possible in the afternoon/evening hours. Moisture will be a bit 
higher across Kauai, so expect more shower activity here with the 
main targets being windward and mauka areas. Showers should
increase statewide Monday night through Tuesday, and possibly into
Tuesday night, particularly in windward areas, as some shortwave
energy moves overhead and some trade wind convergence sets up over
the islands. Showers are expected to be most frequent in windward
areas overnight into the early morning hours, with scattered
shower development occurring in leeward and interior areas during
the afternoon and evening hours. The lighter wind regime Wednesday
through Thursday, will favor showers near the coast at night into
the early morning, and locations over interior and leeward locales
during the afternoons and evenings.

&&

.AVIATION...
With high pressure persisting far north-northwest of the state,
northeast trade winds will remain in the moderate to locally
breezy range through Saturday. Areas of showery low clouds exist
upwind from the isles and will bring MVFR conditions from time to
time, especially in windward and mauka sections. Most of the
precipitation and low ceilings will affect the eastern part of 
the island chain initially, with the western isles possibly 
receiving bouts of showers late this evening and tonight.

AIRMET SIERRA is in effect for north thru east facing sections of
Maui above 2500 feet due to tempo mountain obscuration from low 
clouds and showers.

&&

.MARINE...
Surface high pressure located far northwest of the islands is 
expected to move slowly eastward to a position far north of the 
islands later this weekend. As a result, the trade winds, which 
have been from the northeast, are expected to shift to a more 
typical east-northeast direction by Saturday night. Although the 
winds are not expected to reach the Small Craft Advisory (SCA) 
criteria over any large areas, brief periods of localized near 
SCA conditions can not be ruled out over some of the typically 
windier channels. Heading into early next week, expect the east- 
northeast trade winds to persist through Monday. However, the 
trade winds are expected to gradually weaken from Tuesday through
Wednesday as the surface high pressure system weakens north of 
the islands. As a result, SCA conditions are not expected into 
the middle of next week. 

Surf along north facing shores will trend up through early
Saturday morning as a moderate mid-period north swell continues 
to spread across the area. Surf produced by this swell is 
expected to remain below the High Surf Advisory criteria along 
north facing shores. The north swell will slowly diminish from 
Saturday night through Sunday. The latest model guidance 
continues to show a small, long-period northwest swell arriving 
Monday night. This swell is expected to peak Tuesday night, then 
gradually subside early Wednesday. 

Surf along south facing shores is expected to trend up slightly
this weekend as small south and southwest swells spread across 
the area from sources in the Southern Hemisphere. These swells
will slowly subside from Monday into Tuesday. However, a
long-period south-southwest swell is forecast to arrive late 
Wednesday. Once it arrives, this swell is expected to eventually 
shift to a more southerly direction by Friday, and will likely 
persist into next weekend. 

The weaker trade winds and the lack of a significant upstream 
fetch is expected to keep only small short-period waves along 
east facing shores through most of next week. See the latest 
Collaborative Nearshore Swell and Wind Forecast for Oahu, which 
was issued earlier this afternoon, for details on the various 
swell sources.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Jelsema
AVIATION...Kinel
MARINE...Houston