Area Forecast Discussion for Hawaii

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Issued: Jan 29, 2015 10:07 AM HST

Clouds and a few showers associated with a weak front will move over Kauai and Oahu today, and gradually spread to Maui county tonight and Friday. This moisture will linger through the weekend, and a brief return of light trade winds will focus passing showers over windward slopes, with afternoon clouds over leeward areas. Winds will turn south Monday and then west through midweek with an increase in showers.

A diffuse cold front passing through the islands is bringing a bands of low overcast clouds to the area. This morning, Oahu is currently under one of these cloud bands with cloudy skies prevailing and light to moderate showers moving into the island from the southwest. These clouds and showers are expected to diminish over Oahu this afternoon. Kauai is in a dry slot between cloud bands but low clouds are expected to overtake the garden isle this afternoon with scattered showers. Islands from Maui to the Big Island have relatively clear skies with light southeast flow. Clouds will fill in over the lower elevations of Maui and county and the Big Island as daytime heating progresses. Tonight, some frontal moisture will reach Maui county bringing an increase to clouds and chance of showers over leeward slopes.

Winds will remain light through the weekend but wind direction will spin around the compass as the general flow shifts from SW today, west overnight, north Friday, NE Saturday, east Sunday, and finally back to south Monday. The weak front near the islands today will pull north overnight with a weak ridge filling in north of the islands over the weekend. Moisture from the front will linger over windward areas bringing passing clouds and light/moderate showers through the weekend. For leeward areas over the weekend, afternoon clouds and sea breezes are likely with the sea breezes overpowering the light trades. Nighttime skies will clear with cooler late night temperatures due to radiational heating.

A front approaching from the northwest will turn island winds out of the south Monday into Monday night while pushing the surface ridge south of the islands. Shower coverage will increase with the island topography focusing rainfall over the leeward slopes. Tuesday/wednesday winds shift from the west with west facing slopes catching the majority of rainfall and scattered showers falling elsewhere. These west winds will usher the initial front over the islands Tuesday, with another expected Thursday. The fronts will be a focus of rainfall as they move over the state. Winds over the Big Island summits are also expected to increase around this time. The GFS and ECMWF differ on the timing and strength of these fronts, thus the longer range forecast will potentially be subject to large changes.

A weak front just NW of Kauai, will move through Kauai this afternoon, pass over Oahu this evening and move into Maui county overnight. Predominantly VFR conditions are expected at the terminals, but brief periods of MVFR cigs and -shra will be possible along and ahead of this front.

Airmet sierra is currently in effect for mtn obsc over Oahu. We may be able to drop the airmet for awhile this afternoon, but mtn obsc may become a problem again this evening as the front approaches. Airmets for mtn obsc may be also be needed for Kauai this afternoon as the front moves through.

A moderate NW swell will gradually diminish through tonight. However, reinforcing swells from the NW and NNW will arrive Friday and Saturday respectively, leading to elevated surf along N facing shores, and less so along W facing shores, especially as the swell turns toward the N Saturday. Both swells will produce surf near advisory levels, with surf remaining elevated through Sunday before gradually diminishing Monday and Tuesday. The Oahu surf discussion /srdhfo/ was updated Wednesday and contains detailed insight on the source of the swells.

While winds are expected to remain below small craft advisory /sca/ criteria through at least the weekend, combined seas may top out near 10 feet Saturday in marine zones exposed to the NNW swell.