West Side

Today: Breezy. Mostly sunny with isolated showers. Highs 75 to 81. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 65 to 71. East winds 10 to 20 mph. Chance of rain 40 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Breezy. Isolated showers. Highs 75 to 81. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

South Side

Today: Mostly sunny. Highs around 84. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon.

Tonight: Mostly clear. Lows 62 to 73. North winds up to 15 mph.

Tuesday: Mostly sunny. Breezy. Highs around 84. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon.

North Shore

Today: Breezy. Frequent showers in the morning, then scattered showers in the afternoon. Highs 75 to 80 near the shore to around 64 near 5000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy with numerous showers. Lows around 67 near the shore to around 49 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Breezy. Frequent showers in the morning, then scattered showers in the afternoon. Highs around 78 near the shore to around 65 near 5000 feet. East winds up to 20 mph. Chance of rain 80 percent.

Central Maui

Today: Mostly sunny. Breezy. Isolated showers in the morning. Highs 79 to 85. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Isolated showers. Lows 63 to 68. East winds up to 20 mph. Chance of rain 20 percent.

Tuesday: Breezy. Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs 78 to 84. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Upcountry

Today: Breezy. Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs around 62 at the visitor center to around 64 at the summit. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows around 45 at the visitor center to around 41 at the summit. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 62 at the visitor center to around 65 at the summit. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

East Maui

Today: Breezy. Frequent showers in the morning, then scattered showers in the afternoon. Highs 75 to 80 near the shore to around 64 near 5000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy with numerous showers. Lows around 67 near the shore to around 49 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Breezy. Frequent showers in the morning, then scattered showers in the afternoon. Highs around 78 near the shore to around 65 near 5000 feet. East winds up to 20 mph. Chance of rain 80 percent.

Lanai City

Today: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 71 to 78. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Lows 60 to 65. Northeast winds 10 to 15 mph.

Tuesday: Breezy. Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs 70 to 78. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Kaunakakai

Today: Mostly sunny. Breezy. Isolated showers in the morning. Highs 67 to 84. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 55 to 71. East winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny. Isolated showers in the morning. Highs 67 to 84. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Synopsis

The potential for heavy showers and isolated thunderstorms will exist this morning near or over the Big Island, driven by increasing moisture and an upper disturbance lifting north over the eastern end of the state. Across the rest of the state, a typical trade wind pattern will persist through the first half of the week, with showers favoring windward and mauka areas. However, trades will weaken in the latter half of the week as an upper disturbance and a cold front approach, possibly leading to more widespread rain and thunderstorms.

Discussion

Water vapor imagery shows a broad upper low lifting north toward the Big Island this morning, bringing increasing mid- to upper- level moisture. The combination of lowering upper heights and increasing instability, with steepening mid-level lapse rates and deeper moisture, will keep the threat of heavy showers and isolated thunderstorms in the forecast today. The highest chances for this activity will be this morning over the windward/southeast sections of the Big Island and nearby waters. On the summits, although chances are low, there could be a brief period of wintry mix with this activity early this morning. For the rest of the state, expect typical trade wind conditions, with clouds and showers favoring windward and mauka sections.
Short-term guidance remains in reasonable agreement through the first half of the week, showing rising upper heights over the region as the broad upper low near the Big Island lifts northeast and dissipates. Trades will gradually weaken into the light to moderate range later today through midweek 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.
Confidence decreases later this week through the weekend due to diverging model solutions, but there is general agreement on trade winds being disrupted beginning around Thursday as a cold front approaches and moves into the area. The increasing moisture and instability associated with lowering upper heights and the front will raise the potential for showers and thunderstorms.

Aviation

Winds should trend downward through mid-week with the passage of a front to the north and another front approaching the islands. Low cigs and SHRA should favor windward and mauka locations. MVFR conds expected in SHRA otherwise VFR should prevail.
AIRMET Sierra continues for mtn obsc along windward sections of the all islands.
AIRMET Tango continues for mod to isol severe upper level turb from Maui to the Big Island, and will likely be needed through the morning hours.

Marine

Surface high pressure far northeast of the waters will drive moderate to fresh trade winds today before easing 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 may bring the potential for thunderstorms over the southern coastal and offshore waters through the morning hours. A light wind regime is expected by Thursday through the end of the week as a potential cold front moves down the island chain.
Surf along north and west facing shores will remain small to moderate through the morning hours before a moderate long-period northwest swell is expected to fill in through the day. Guidance from the ECMWF and observations at NDBC offshore buoy 51101 is showing a slower arrival than previously forecasted. The High Surf Advisory (HSA) has been delayed for a start time at noon today 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 into Tuesday 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.

HFO Watches/Warnings/Advisories

High Surf Advisory from noon today to 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.

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Data Courtesy of NOAA.gov