textproduct: Honolulu

SYNOPSIS

Light to moderate trade winds will prevail for the next few days, followed by increasing trade wind speeds this weekend. Meanwhile, an upper disturbance just to the northwest will enhance showers over the western end of the state for the next couple of days, and could produce a few thunderstorms in the western coastal waters as well. The focus for increased showers will shift to the eastern end of the state this weekend as an area of tropical moisture passes by.

DISCUSSION

Water vapor imagery shows an upper low west of the main Hawaiian Islands this morning. This feature is generating instability and wind shear resulting in scattered thunderstorms around 50 miles west of Niihau. Guidance keeps the activity over the coastal waters just west of the islands today and Thursday, which the current forecast depicts. However, enhanced showers are expected today across Kauai (and Oahu to a lesser extent) as the instability creeps onto the western end of the state. The upper low is forecast to lift away to the north on Friday, returning more stable conditions to the area.

Meanwhile, trade winds will remain at only light to moderate speeds for the next couple of days as the remnants of former Tropical Cyclone Genevieve have cut off the high pressure to our north, interrupting the trade wind flow. The weaker trades will likely result in localized sea breezes each afternoon, bringing increased cloud buildups and a few showers each afternoon. Showers will be more prominent across Kauai and Oahu due to more available moisture and instability. By the weekend, trade winds will increase back to locally breezy levels.

The forecast becomes more interesting again this weekend as model guidance continues to suggest that a plume of moisture will either move over or very near the eastern end of the state late Saturday into Sunday. Despite most guidance keeping the bulk of the moisture just south of the state, it is likely that at least some of the enhanced tropical moisture will become embedded within the trade wind flow, increasing showers for Maui and the Big Island.

AVIATION

A weak high pressure ridge far north of the state will maintain gentle trade winds in the forecast. Overall, a fairly dry day is expected during the day today but a few showers will be possible especially over and around Kauai. Due to the gentle trade winds, sea breezes could develop later this morning, which would allow for afternoon clouds and a few showers over select leeward slopes.

An upper level disturbance is producing scattered thunderstorms just west of Kauai this morning. SIGMET XRAY is in effect for the potential of severe turbulence associated with these thunderstorms. The threat for thunderstorms should stay west of Kauai and is expected to dissipate by this afternoon.

AIRMET Sierra in effect for mountain obscuration above 020 for the entire island of Kauai. This AIRMET will likely be cancelled later this morning.

MARINE

Moderate trades persist as surface troughing to the NE maintains a rather weak pressure gradient over the state. Dissipation of the trough to the NE combined with renewed trough development S of the islands will favor breezy trades by week's end. The resident upper level low is supporting ongoing isolated thunderstorms NW of Kauai in the vicinity of the nearshore waters this morning. This activity is forecast to diminish through the day.

Surf along S shores remains below the seasonal average. By this weekend a small, long period S swell arrives followed by a series of reinforcing swells that will boost surf toward seasonal averages heading into next week.

Small, medium period E swell generated from former Tropical Cyclone Genevieve lingers, but will ease through today. Moderate trades maintain short period chop.

Surf along N and W shores remains flat to tiny through the period except for locales exposed to trade wind swell

HFO WATCHES/WARNINGS/ADVISORIES

None.