Marine Weather and Tide Forecast for Lahaina, HI

DISCUSSION
A broad upper level low can be seen just southeast of the Big Island on water vapor imagery this morning. The proximity of this feature along with its associated instability and increased moisture aloft will maintain the potential for heavy showers and isolated thunderstorms through the morning and possibly into the afternoon. The highest chances for this activity will be through this morning over the windward/southeast sections of the Big Island and nearby waters, but diabatic heating may help to sustain this activity through the afternoon and bring possible development over leeward slopes. On the summits, a dusting of snow/ice can be seen on the webcams, and a wintry mix is expected to continue through the morning with this activity. For the rest of the state, expect typical trade wind conditions, with clouds and showers favoring windward and mauka sections.

The upper level low will continue to lift northeast and begin to dissipate throughout the day and into tonight. As it does so, mid level ridging will edge over the state from the west, increasing atmospheric stability. Trade winds will weaken into the moderate to locally breezy category later today and persist through Wednesday as the surface ridge weakens and shifts southward, following a front passing to the north. This setup will result in a mainly stable and dry trade wind pattern, with the best chances for showers in windward and mauka areas during the night and early morning hours.

The next pattern shift is expected to occur on Thursday as a cold front approaches from the northwest, disrupting the trades.
Beyond Thursday, forecast confidence decreases due to diverging model solutions, but there is general agreement on the front moving into the western end of the state sometime Thursday night into early Friday morning. Increasing moisture and instability associated with lowering upper heights will increase the potential for showers and thunderstorms as the front moves into the area.

AVIATION
An upper low southeast of the Big Island will enhance showers and bring isolated thunderstorms to the Big Island and surrounding waters. AIRMET Sierra is posted for tempo mountain obscurations above 2500 feet over windward slopes this morning. This AIRMET will likely continue through the day. Clouds and enhanced showers may form over leeward slopes this afternoon with the possibility of needing AIRMET Sierra for the leeward side later today.

Elsewhere, trade winds will weaken slightly into Tuesday as a cold front passes north of Hawaii. Winds will focus clouds and showers over windward and mauka areas that will produce isolated mountain obscurations.

MARINE
Surface high pressure far northeast of the waters will drive moderate to fresh trade winds today. Winds will ease slightly tonight as the ridge to the north weakens and a front passes by to the north. An upper level disturbance south of the Big Island will bring the potential for thunderstorms over the southern offshore waters through tonight. Winds will weaken further and become increasingly variable later in the week when a weak cold front approaches from the northwest and moves down the island chain.

A moderate long-period long- period northwest swell is expected to quickly build in later today. A High Surf Advisory (HSA)
remains in effect noon today through Tuesday for north and west facing shores of Niihau, Kauai, Oahu, and Molokai and north facing shores of Maui. The swell is expected to peak late tonight or Tuesday morning before slowly declining through the week.

An even larger, long- period northwest swell that could potentially bring High Surf Warning level conditions for most north and west facing shores is expected Friday into Saturday from a closer, stronger storm that tracks generally towards the islands over the next few days.

Surf along east facing shores will hold relatively steady today then continue to decline through the end of the week. A small north swell could potentially elevate exposed shorelines Wednesday and Thursday. South shore surf will remain very small through the middle of the week. An out of season long-period south swell may move through the islands at the end of the week, bringing a sizable boost to south shore surf.

FIRE WEATHER
No critical fire conditions anticipated during the forecast period as low-level moisture remains sufficient and wind speeds remain below critical thresholds. In addition, a front could bring a period of more widespread rainfall to the islands around the end of the week.

HFO WATCHES/WARNINGS/ADVISORIES
High Surf Advisory until 6 PM HST Tuesday for Niihau-Kauai Leeward-Waianae Coast-Oahu North Shore-Maui Windward West-Kauai North-Molokai Windward-Molokai North-Molokai West-Maui Central Valley North-Windward Haleakala.