textproduct: Honolulu

SYNOPSIS

Breezy trade winds will continue through most of the week. A lingering weak trough near the western end of the state will result in a bit more clouds and showers for Kauai versus the other islands through mid-week. Otherwise, showers will generally favor windward and mauka areas, most frequently at night and during the early morning hours. An upper level disturbance may bring a slight uptick in trade wind shower coverage late this week into the weekend.

DISCUSSION

Early this morning, satellite and radar imagery continues to show low clouds and showers upstream of Kauai embedded within the trade wind flow approaching and moving over the Garden Isle as a weak surface trough continues to linger near the western end of the state. This trough has supported more widespread cloud coverage and numerous showers over Kauai and its adjacent waters throughout the night, a trend that will continue throughout the day. Elsewhere, showers and low clouds embedded within the moderate to locally breezy trade wind flow moving into primarily windward and mauka sections of the islands have been more isolated to scattered in nature.

The weak trough near the western end of the state is forecast to gradually lift north and dissipate by Wednesday. Otherwise, ridging at the surface and aloft will maintain stable, breezy trade wind weather across the state through at least Thursday with isolated to scattered showers favoring windward and mauka areas.

Near the end of the week (Friday into the weekend), confidence in the forecast decreases a bit as model guidance diverges. While the consensus is that that a mid- to upper- level cutoff low will develop in the vicinity of the islands, there are some significant differences among the global models as to the location of this feature (for example, the ECMWF depicts it well northeast of the islands while the GFS places it very close to, or even just west of, Kauai). Regardless, instability looks to increase as temperatures aloft cool, potentially increasing trade wind shower activity to end the week.

AVIATION

Stable trade wind weather will persist the next several days. Isolated to scattered showers trapped within trades will primarily focus upon windward exposures and likely have more of an impact on Kauai and Big Island this morning.

AIRMET Sierra remains in effect for mountain obscurations above 3000 feet along north through east areas on Kauai. Brief overnight VFR cat mountain obscuration is possible across remaining island windward locations.

AIRMET Tango remains in effect for both lower level turbulence downstream of island terrain and westerly upper level turbulence passing over the state.

MARINE

High pressure remains in place north of the Hawaiian Islands into the first half of next week, keeping fresh to locally strong trades blowing through Thursday. An upper level disturbance moves into the Hawaii region from the north from Friday into the weekend. Expect increasing clouds and shower trends along with a slight decrease in trade wind speeds as a low level trough develops over the islands. The Small Craft Advisory was extended through Wednesday afternoon, and will likely continue into Thursday for the typical windier waters and channels near Maui and the Big Island.

A small short to medium period northwest (330 deg) swell will slowly decrease through tonight. The next small long period northwest swell arrives into the western islands by Wednesday afternoon, peaking on Thursday, then slowly fading into Friday. Expect small surf to continue along north and west facing shores of the western islands at least into Thursday.

The small long period south swell energy will continue to show a slow decline through the week with the period dropping by 1 second each day. The next small long period south swell arrives on Saturday, keeping surf heights elevated along south facing shores. Slightly elevated surf along E facing shores continues until trades weaken this weekend.

HFO WATCHES/WARNINGS/ADVISORIES

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