textproduct: Honolulu

SYNOPSIS

A high pressure system will remain far north of the Hawaiian Islands will keep trade winds in the moderate to locally windy range through Tuesday. A low level trough passing through the islands tonight will keep enhanced showers in the forecast favoring the windward mountain slopes of Maui and the Big Island in the overnight to early morning hours. Medium range model solutions are showing a deepening low setting up just north of the island chain from Thursday onward, potentially increasing shower activity from Friday into the weekend.

DISCUSSION

The satellite imagery this morning shows deeper low level clouds banking up against the windward mountains of each of the larger islands in the chain. These unstable clouds are driven up the mountain slopes by the trade winds producing periods of showers for communities near or just leeward of these windward island mountains. Traditionally drier leeward areas will still see some brief passing showers, just less frequent and lower rainfall amounts. Any showers that develop will favor the early morning hours, with the typical diurnal drying trends for the late morning and afternoon time periods.

In the big picture, a strong high pressure system will linger just north of the Hawaiian Islands through Wednesday, keeping moderate to locally windy trade winds in the forecast through Tuesday. Trade wind speeds will show weakening trends from Wednesday to Thursday as a cut off low pressure system deepens and drifts eastward just north of the islands. The latest track of this cold core low has shifted farther northeast of the islands, decreasing chances for southerly winds and more significant rainfall activity for Friday into next weekend time periods. Trade wind speeds will weaken from Friday onward as the low passage north of the islands disrupts the large scale high pressure gradient over the Hawaii region.

We will continue to closely monitor this system as both the track and intensity will evolve over time. Bottom line on this system: The closer the low tracks relative to the islands, the wetter the weather pattern will become. Stay tuned.

AVIATION

Breezy trades will persist through the forecast period. Isolated to scattered showers will be mainly concentrated mainly along windward and mauka locations, most numerous this morning and late tonight. These showers may produce brief periods of MVFR ceilings and visibility.

AIRMET Sierra remains in effect for north through east sections of the Big Island, Oahu, Maui, and Molokai above 2500 feet due to low clouds and showers. However, by mid-morning, SIERRA will likely be dropped.

AIRMET Tango remains in effect for for tempo moderate turbulence downwind of terrain below 9000 ft.

MARINE

Robust surface high pressure centered far north of Hawaii will maintain fresh to strong trade winds at current strength for the next couple of days, and a Small Craft Advisory (SCA) remains in effect for all waters except windward Big Island through early Tuesday. Trades will steadily decrease late Tuesday and Wednesday as the high weakens and is displaced eastward by an approaching low far northwest of the islands. The SCA will likely be trimmed back to the typically windy waters around Big Island and Maui at that time. Trade winds will lower to gentle strength, or may become disrupted, as the low passes to the north Thursday and Friday.

A north-northwest swell and a smaller overlapping west-northwest swell will slowly decline today and fade on Tuesday. A very small northwest swell may arrive Thursday, followed by a moderate north- northwest swell next weekend.

The current south swell will continue a slow decline today. South shore surf will drop below seasonal average and will remain relatively small through much of the week. A moderate south- southwest swell is expected next weekend.

Rough trade wind swell will produce east shore surf just above seasonal average through Tuesday, then decline later in the week as trade winds decrease.

FIRE WEATHER

Fire weather will remain below critical levels for the next several days. The subsidence temperature inversion near Maui and the Big Island today will drop into the 7000 to 8000 foot range.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 AM HST Tuesday or most Hawaiian coastal waters and channels.