Hilo

Tonight: Mostly cloudy. Scattered showers in the evening, then occasional showers after midnight. Lows 64 to 70 near the shore to 54 to 59 at 4000 feet. Southeast winds up to 10 mph shifting to the west after midnight. Chance of rain 90 percent.

Monday: Mostly cloudy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 79 to 85 near the shore to around 66 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 80 percent.

Monday Night: Mostly cloudy with numerous showers. Lows 64 to 70 near the shore to 53 to 60 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Kona

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 74 near the shore to 49 to 55 near 5000 feet. Light winds. Chance of rain 30 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 87 near the shore to around 69 near 5000 feet. Light winds becoming northwest up to 10 mph in the afternoon. Chance of rain 40 percent.

Monday Night: Partly cloudy. Isolated showers in the evening. Lows around 75 near the shore to 48 to 55 near 5000 feet. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy with scattered showers. Lows 64 to 73 near the shore to 57 to 64 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs 66 to 85. East winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. Chance of rain 50 percent.

Monday Night: Breezy. Mostly cloudy with scattered showers. Lows 64 to 72 near the shore to 57 to 64 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Kohala

Tonight: Mostly cloudy with scattered showers. Lows 64 to 73 near the shore to 57 to 64 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs 66 to 85. East winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. Chance of rain 50 percent.

Monday Night: Breezy. Mostly cloudy with scattered showers. Lows 64 to 72 near the shore to 57 to 64 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

South Big Island

Tonight: Breezy. Mostly cloudy with isolated showers. Lows around 76 near the shore to around 54 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Monday: Windy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 86 near the shore to around 68 near 5000 feet. East winds 10 to 30 mph. Chance of rain 20 percent.

Monday Night: Mostly clear. Breezy. Isolated showers in the evening. Lows around 74 near the shore to around 52 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy. Scattered showers in the evening, then occasional showers after midnight. Lows 64 to 70 near the shore to 54 to 59 at 4000 feet. Southeast winds up to 10 mph shifting to the west after midnight. Chance of rain 90 percent.

Monday: Mostly cloudy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 79 to 85 near the shore to around 66 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 80 percent.

Monday Night: Mostly cloudy with numerous showers. Lows 64 to 70 near the shore to 53 to 60 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Waikoloa

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 75 near the shore to around 55 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 85 to 91 near the shore to 67 to 74 above 4000 feet. East winds up to 15 mph shifting to the north in the afternoon. Chance of rain 20 percent.

Monday Night: Partly cloudy. Isolated showers in the evening. Lows around 75 near the shore to 52 to 57 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Ample moisture and unstable conditions will result in continued potential for enhanced showers across all islands tonight, and isolated thunderstorms for the western end of the state through Monday night. Some showers could be heavy at times, and a Flood Watch remains in effect for all Hawaiian Islands through tonight. A drier and more stable trade wind pattern will return from Tuesday onward.

Discussion

This afternoon, water vapor imagery shows a low aloft centered near Lanai. Deep moisture remains in place over the state with precipitable water near or above 2.0 inches. This moisture, combined with instability provided by the upper low, will continue to support shower chances and even isolated thunderstorms across portions of the state into this evening and tonight. Guidance suggests that the moisture and instability could linger near the western end of the state into Monday and Monday night as well as the upper low slowly moves westward and washes out over the next 24 to 36 hours. With this in mind, isolated thunderstorms have been added to Kauai and surrounding waters through Monday night with this afternoon's forecast updates.
Although most of the heavier rainfall has remained offshore today, it remains possible that bands of heavier showers could move onshore as the low continues to slowly move westward. Should any of these showers become anchored on the terrain, flooding will remain a possibility. Although there is some uncertainty regarding where or when this could occur, the potential justifies extending the Flood Watch in time through at least tonight. As the area of greatest rainfall potential gradually shifts westward to the western end of the state by Monday, further adjustments to the Flood Watch may be needed. As ridging builds and trades remain locally breezy over the next few days, the areas of greatest, most intense rainfall will be windward and mauka areas. However, sheltered leeward locations could also see some moderate to heavy showers, particularly through early this evening and again tomorrow afternoon.
Meanwhile, over the Big Island summits, snow that occurred early this morning largely melted during the day as temperatures hovered just above the freezing mark. However, with ample moisture lingering in the area and with temperatures expected to once again drop near or below freezing tonight, some additional snowfall and/or ice accumulation will be possible. Therefore, the Winter Weather Advisory for the Big Island summits will continue through tonight.
As the upper low washes out Tuesday and Wednesday, a breezy and increasingly more stable trade wind regime is expected. Pockets of higher mid-level moisture riding in on trades will contribute to intermittent increases in windward shower activity throughout the rest of the week.

Aviation

The potential for heavy showers and thunderstorms will remain in the forecast tonight into Monday as a broad upper low lingers over the region. Much of the shower activity this afternoon has broken up a bit and shifted offshore, and have therefore cancelled all AIRMET Sierra for all portions of the state. Clouds and showers could start to anchor along mountains later tonight for potentially any island, so will be watching to see if AIRMET Sierra need to be issued again. Otherwise, expect VFR conditions through the early evening with isolated/brief mountain obscurations in showers.
AIRMET Tango is posted for tempo moderate low-level turbulence downstream of island terrain below 8000 feet due to the strengthening trades.

Marine

High pressure building far NE of the islands will persist through the week, supporting moderate to locally strong trade winds. A Small Craft Advisory for waters around Maui County and the Big Island will likely remain in effect for the foreseeable future. A low aloft currently near Maui County will drift slowly SW, then W, over the next couple of days. Instability associated with the low will bring the potential for locally heavy showers and/or thunderstorms through Monday, with the potential shifting westward with the low.
A small, medium-period N swell will build tonight, persist into Monday, then gradually decline while another small N swell arrives on Tuesday. A small NW swell is possible Thursday, with potential for a bigger, long-period NW swell next weekend. A small long- period S swell will slowly decline through midweek.
Surf will remain somewhat elevated along E facing shores the next couple of days – due to the combination of small long-period E swells generated by former major hurricane Kristy, and increasing short-period wind waves as trade winds build. NDBC buoy 51004 SE of the Big Island and PacIOOS nearshore buoys are detecting increases in this expected long-period energy from the E.

HFO Watches/Warnings/Advisories

Flood Watch through 6 AM HST Monday for all Hawaiian Islands.
Winter Weather Advisory until 6 AM HST Monday for Big Island Summits.
Small Craft Advisory until 6 PM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov