textproduct: Honolulu

SYNOPSIS

A weak surface trough will continue to move west of Kauai today. This feature will bring a slight uptick in afternoon shower activity, especially over interior and northwest portions of Oahu and Kauai. Elsewhere, isolated to scattered showers will be mainly confined to interior regions and on mountain slopes as weak to moderate east southeast flow prevails. Through this weekend, expect weak to moderate east or east southeasterly flow statewide with mainly isolated showers along windward slopes. Monday into mid- next week, trade winds increase, along with a return of more consistent night and early morning showers for windward locations.

DISCUSSION

IR Satellite showed scattered to broken low clouds meandering just west of Kauai this morning, associated with a surface trough, with mostly clear skies elsewhere. This trough will be the main driver feature in today's weather as it slowly creeps further westward, away from the state. Loose surface pressure gradients surrounding Kauai will allow for another day of light morning winds followed by afternoon sea breeze development. Winds will start off light on Oahu, before light to moderate east southeast flow fills in as the day progresses. This will likely lead to a modified afternoon sea breeze pattern along leeward areas. Moderate to locally breezy east southeast flow expected for the remaining islands as the trough pulls further away. Statewide, relatively muggy conditions should persist, as dewpoints are forecast in the low 70s. For Oahu and Kauai, latest hi-res guidance once again shows diurnally driven showers forming over interior/mountainous regions by early afternoon, then spreading out in coverage, mainly over the northwest portions of both islands. Residual moisture and weak instability left over from the passing trough may allow for a brief pockets of moderate to heavy rain embedded in the showers. Thus, the issuance of a stray Flood Advisory remains possible if a robust shower stalls, or anchors over the terrain. Expect diurnally driven afternoon showers for Maui County and the Big Island as well, mainly over the mountain slopes and higher terrain. Rainfall activity and cloud cover should dwindle by tonight with the loss of diurnal heating.

Saturday into Sunday, moderate east southeast flow slowly backs to easterly flow statewide with some shower activity along windward areas during the nights and early mornings. Dewpoints will gradually lower from the lower 70s to upper 60s through the weekend making it feel a bit less sticky and more comfortable.

By Monday, latest runs of both the GFS and ECMWF dig an upper level trough southward, northeast of the islands. Late Monday into Tuesday, these long range models cut an upper low off from the trough. For the remainder of the week, the GFS is more bullish on pulling the low to the southwest and over the state, as well as inducing a weak surface trough. This would act to weaken the capping inversion and enhance trade wind showers on all islands. The ECMWF has the low drifting westward, passing north of the island chain with slightly less influence on our local weather. Either way, both models indicate a moderate to breezy trade wind pattern with wetter conditions ensuing on windward areas mid- to late next week.

AVIATION

Skies are gradually clearing across the islands this morning as a surface trough departs the area. Winds will remain relatively light across most sites, with a mix of land/sea breezes and trades prevailing through the period. VFR conditions are broadly expected.

AIRMET Sierra remains in effect for Kauai and Oahu due to mountain obscuration from showers. Conditions are expected to improve later today, however.

MARINE

Light to moderate trades will hold for the next few days as a weak surface ridge remains to the northeast and a broad surface trough lingers north of the island chain over the next few days. The weak trough, which moved across the islands over the past several days, is now north of Kauai, producing scattered showers over the offshore waters. Trade winds will begin to increase on Monday and trend upward through next week as troughing north of the island chain is replaced by a strengthening ridge.

A moderate, medium period south swell will steadily fade today into the weekend, allowing surf along south and west-facing shores to steadily diminish through Saturday. After this, a series of smaller south and southeast swells will fill in Saturday into the first half of next week, which will maintain surf near seasonal averages through next week.

Tiny surf will prevail on north shores through most of the coming week as only some limited short-period energy reaches the islands from the north. Trade winds remain lighter than normal through the weekend, keeping surf along east-facing shores below average. East shore surf will begin to slowly trend up beginning Monday as trade winds increase across the region.

HFO WATCHES/WARNINGS/ADVISORIES

None.