textproduct: Honolulu

SYNOPSIS

A drier and less humid trade wind flow will continue to fill in over the state today. Shower activity will be focused across windward areas and will become less frequent, though leeward Big Island may still experience scattered briefly heavy showers in the afternoon. A tropical disturbance moving within the trade winds may bring increased humidity and showers again late Tuesday or Wednesday.

DISCUSSION

A drier air mass is slowly developing over the state on moderate trade winds. The bulk of a diffuse band of moisture has moved west of the islands, but some moisture remains hung up on Big Island and Kauai. Overnight, generally less than a quarter of an inch of rainfall has been measured on windward areas of these islands, and showers remained rather active over the South Kona District of the Big Island. Little rainfall occurred on windward Oahu and Maui County overnight, and dry leeward areas of these islands have been dry.

Expect a drier and less humid day over most of the island chain today. Moderate trade winds will push the bulk of the deeper moisture west of the islands, allowing leeward dew points to fall into the mid 60s and bringing relief from high humidity of the past several days. Typical light to moderate scattered showers are expected over windward areas, but rainfall accumulation will be low. Spotty afternoon showers, some briefly heavy cannot be ruled out on leeward Big Island and to a lesser degree on leeward Kauai.

Moderate trade winds will bring rather typical trade wind weather this weekend through early next week. A weak upper-level trough will linger over the area, keeping modest instability and a weak inversion over the state. As a result, there will be a chance of a few heavy showers over the Kona slopes of Big Island each afternoon and evening.

A tropical disturbance moving within the trade winds may bring increased humidity and showers again late Tuesday or Wednesday. Differences in timing and placement of this moisture persist between the GFS and ECMWF, which is keeping the details elusive at this point. This moisture could persist through Thursday of next week. Beyond that, there is significant uncertainty regarding the future location and timing of east Pacific Tropical Storm Norbert, which may be near the islands late in the week.

AVIATION

The trade winds be moderate to breezy this morning, with a few showers lingering around the Big Island. Heavier precipitation can be found offshore, moving westward. Satellite imagery remains a bit messy, with a mix of low, mid, and high level clouds. TAF sites depict this as well, with cigs varying from 2500ft to 6000ft in addition to high clouds and some sites being VFR. Current thinking is that the current clouds will linger through the early morning and improve later in the day. The windward sides of islands may struggle a bit with cloud clearing, as showers remain in the forecast.

AIRMET Sierra remains for the Big Island, Maui, Oahu and Kauai through the morning. Isolated showers remain in the forecast, with the windward sides of these island potentially seeing additional showers.

MARINE

Moderate to locally fresh trade winds expected for next few days as a weak N-S oriented trough has moved west of Kauai. A couple of troughs far northeast and southeast will keep a weak pressure gradient across the state through the weekend. The trough from the southeast will near the state Saturday allowing winds to shift out of the northeast through early next week.

A moderate mid-period south swell will continue to steadily decline over the next few days with below average surf expected by the weekend. Background southerly swells will keep surf from going flat over the weekend into early next week. A gale low just east Australia will shift east of New Zealand over the next couple of days in a more favorable position for more consistent south swells for Hawaii late next week. Forerunners from the captured fetch from this system could start trickling in by mid week and gradually build through the rest of the week into next weekend, generating above average surf.

On east facing shores expect seasonal average surf that was caused by former tropical cyclones to gradually fade to below average by Saturday and hold into early next week as trades locally and upstream remain disrupted.

Tiny surf along north facing shores as the swell from Lowell continues to decline.

FIRE WEATHER

Fire weather risk will remain low the next several days due light to moderate winds and the effects of recent rainfall, even as afternoon relative humidity falls below 50 percent over many leeward areas. Inversion heights are expected to remain elevated or weak through Monday.

HFO WATCHES/WARNINGS/ADVISORIES

None.