251 
FXHW60 PHFO 080625
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
825 PM HST Thu May 7 2020

.SYNOPSIS...
A trade wind weather pattern will continue through the weekend, due 
to high pressure far north of the area. Clouds and passing showers 
will favor windward and mauka areas, with a few showers briefly 
spreading to select leeward locations. Winds will become weaken 
toward the middle of next week as the high moves to a position far 
northeast of the area. 

&&

.DISCUSSION...
A 1027 mb high far NW of the islands is supporting moderate to 
locally breezy NE trade winds, with embedded moisture providing 
passing showers over windward and mauka areas. Winds are 
sufficiently strong enough to blow a few showers to some leeward 
locations. This general weather pattern is expected to persist 
through the weekend as the eastward-moving surface high passes far N 
of the islands, allowing winds to shift to the E. As the high moves 
into the NE Pacific Tuesday and Wednesday, a front will pass far N 
of the area, and winds will diminish, likely becoming light and 
variable over land through the end of the week. 

A low aloft is forecast to develop W of the area late in the 
weekend, then pass over the islands on Monday. This feature will 
likely destabilize the island atmosphere, and potentially lead to 
increased shower coverage and intensity, especially windward and 
mauka. After the low departs to the NE Tuesday, a trough aloft may 
linger near islands through mid-week. Afternoon and evening clouds 
that form over the islands in response to daytime heating/sea breeze 
convergence will likely drop a few showers.  

&&

.AVIATION...
A moderate northeast trade wind flow will continue into Friday as an 
area of high pressure remains far northwest of the main Hawaiian 
Islands. VFR will be the prevailing flying condition overnight, 
although there will be brief periods of MVFR ceilings and vis 
associated with embedded showers riding in with this northeast wind 
flow. Satellite and radar show scattered low clouds and showers 
extending far upwind of the islands east of Oahu, and this is where 
most of the showers will be overnight. To a lesser degree, Oahu and 
Kauai will get a stray shower or two. The showers will not be 
limited to the windward and mountain areas, as the trades are strong 
enough to carry the showers well into the lee areas of the smaller 
islands. The evening clouds covering mainly the lower half of 
leeward Big Island, will slowly clear out. A shower or two is 
possible overnight along the coastline there and adjacent waters. 
Tops of the showers are around 10k feet with higher tops to 15k feet 
in the heavier showers.

No AIRMETs are currently in effect.

&&

.MARINE...
Moderate to fresh northeast trade winds will continue through 
Friday, then shift out of the east over the weekend as high pressure 
builds north of the islands. Although Small Craft Advisory-level 
winds are not expected, brief periods with pockets of fresh to 
strong breezes can't be ruled out across the windier areas and 
channels. For next week, guidance shows a weakness in the ridge 
developing as a front passes far to the north. If this evolves, 
light winds will become a possibility by the midweek time frame. 

Surf along north facing shores will trend up later tonight through 
Friday as a moderate northerly swell arrives from a gale that passed 
far north of the state over the past few days. This source should 
hold through Saturday, then fade through the day Sunday. Low 
pressure that has developed over the far northwest Pacific near the 
Kurils (around 2500 nm away from the islands) has intensified into a 
storm over the past 24-hrs. Recent satellite data reflected this and 
showed a favorable fetch aimed at the islands within the 300-310 deg 
directional band. Guidance remains in decent agreement and shows a 
small, long-period west-northwest swell arriving from this source by 
Tuesday. 

Surf along south facing shores will trend up Friday through the 
weekend as a small south and southwest swell fill in from recent 
southern hemisphere activity. Looking ahead into next week, latest 
data and analysis showed a decent sized fetch setting up over 
Hawaii's swell window southeast of New Zealand today. An altimeter 
pass showed seas in this area up to 30 ft. As this system continues 
eastward across the far southern Pacific this weekend, guidance 
shows this fetch aimed at the islands holding. As a result, a long-
duration event seems possible that should begin around Wednesday, 
then carry into next weekend (15th/16th) as the swell shifts more 
out of the south.

Surf along east facing shores will remain small into the weekend due 
to the lack of trades upstream of the state across the eastern 
Pacific. A downward trend appears possible by midweek as the trades 
diminish.

&&

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

&&

$$

DISCUSSION...Birchard
AVIATION...Lau
MARINE...Gibbs