Photo Credit: James Grenz

Hilo

Today: Cloudy with numerous showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 80 to 85 near the shore to 66 to 72 at 4000 feet. Southeast winds 10 to 15 mph decreasing to up to 10 mph in the afternoon. Chance of rain 70 percent.

Tonight: Cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 64 to 71 near the shore to 56 to 61 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Monday: Mostly cloudy with numerous showers. Highs 78 to 83 near the shore to 64 to 70 at 4000 feet. South winds up to 10 mph in the morning becoming light. Chance of rain 70 percent.

Kona

Today: Cloudy. Scattered showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 82 to 87 near the shore to around 69 near 5000 feet. East winds around 10 mph in the morning becoming light. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 70 to 75 near the shore to 50 to 57 near 5000 feet. Northeast winds around 10 mph in the evening becoming light. Chance of rain 30 percent.

Monday: Partly sunny with scattered showers. Highs 81 to 86 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Today: Cloudy with numerous showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 65 to 83. Southeast winds around 10 mph in the morning becoming light. Chance of rain 70 percent.

Tonight: Cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 64 to 69 near the shore to 57 to 64 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Monday: Mostly cloudy with numerous showers. Highs 64 to 83. Light winds. Chance of rain 70 percent.

Kohala

Today: Cloudy with numerous showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 65 to 83. Southeast winds around 10 mph in the morning becoming light. Chance of rain 70 percent.

Tonight: Cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 64 to 69 near the shore to 57 to 64 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Monday: Mostly cloudy with numerous showers. Highs 64 to 83. Light winds. Chance of rain 70 percent.

South Big Island

Today: Cloudy with numerous showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 83 near the shore to around 68 near 5000 feet. East winds 10 to 15 mph in the morning becoming light. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows around 72 near the shore to around 53 near 5000 feet. East winds 10 to 20 mph. Chance of rain 30 percent.

Monday: Partly sunny with scattered showers. Highs around 83 near the shore to around 66 near 5000 feet. Northeast winds around 10 mph. Chance of rain 40 percent.

Puna

Today: Cloudy with numerous showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 80 to 85 near the shore to 66 to 72 at 4000 feet. Southeast winds 10 to 15 mph decreasing to up to 10 mph in the afternoon. Chance of rain 70 percent.

Tonight: Cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 64 to 71 near the shore to 56 to 61 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Monday: Mostly cloudy with numerous showers. Highs 78 to 83 near the shore to 64 to 70 at 4000 feet. South winds up to 10 mph in the morning becoming light. Chance of rain 70 percent.

Waikoloa

Today: Cloudy. Scattered showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 81 to 87 near the shore to 67 to 72 above 4000 feet. East winds around 10 mph in the morning becoming light. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 70 to 75 near the shore to 51 to 57 above 4000 feet. East winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs 81 to 86 near the shore to 65 to 70 above 4000 feet. Light winds. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Wet weather will move into the state today through Monday morning as a weakening cold front drifts into the western islands and a tropical moisture plume moves up from the south into the eastern and central islands. A strong upper level trough will produce periods of heavy rainfall and isolated thunderstorms across the region. Conditions will begin to stabilize from Monday morning onward with enhanced rainfall lingering over portions of Maui County. Drier trends will start late Monday as the upper trough passes eastward through the island chain. High pressure will build back into the region from Tuesday onward with more stable conditions in light and variable winds.

Discussion

Satellite imagery this morning shows a cold front stalling northwest of Kauai with isolated thunderstorms developing just ahead of the frontal trough. An upper trough just northwest of the islands will move from west to east across the region. A tropical plume of moisture continues to stream up into Hawaii and Maui Counties. Radar imagery this morning shows showers moving up into south and east sections of Maui. Stronger showers are developing further south of Maui County drifting northward.
A weakening cold front and upper level trough are approaching Kauai from the northwest this morning. Low level convergence bands are developing ahead of the frontal trough that will increase shower activity across the western islands of Kauai, Niihau and Oahu as the upper trough enhances instability across the region. This frontal trough will diminish and stall near Kauai later today. Weather wise, expect increasing shower activity with numerous showers ramping up over these islands through the morning hours. Periods of heavy showers will develop over some areas with isolated thunderstorm potential.
Light southerly winds over the eastern half of the state continues to pull up some deeper tropical moisture into Hawaii and Maui Counties. The combination of increasing low level moisture with a trough moving into the region from the west will enhance showers and thunderstorms over the Big Island through the afternoon. The Big Island will see decreasing shower trends from tonight onward. For Maui County the position of this tropical moisture plume and upper trough will produce widespread showers through Monday morning. Heavy showers are forecast in some areas with the potential for isolated thunderstorms across Maui County. Weather trends improve by late Monday morning for Maui County as the upper trough weakens and the deeper moisture drifts eastward.
A Flood Watch was issued for all Hawaiian Islands this morning due to increasing potential for slow moving heavy showers. We are already seeing some of these shower bands training (multiple storms following the same path) near Kauai and Maui this morning. Terrain anchored thunderstorms are also possible in some areas through tonight. Small scale convergence bands under the upper trough will drive much of the convective forcing with some areas experiencing more shower activity than others. Heavy showers will favor these low level convergence bands producing from 1 to 4 inches of rainfall over a short time period. Forecasting where and when these heavier showers will develop is challenging with this weather pattern, thus we decided to include all islands in the Flood Watch for today and tonight.
High pressure will build back in over the islands with more stable trends and continued light to moderate background east to southeast winds from Tuesday through next weekend. Land and sea breezes will continue over portions of each island and easterly background winds will favor brief passing shower activity over windward and mountain slopes.

Aviation

A trough west of Kauai will interact with a moist airmass moving over the islands from the south during the next 24 to 36 hours. By this afternoon, shower coverage will increase state wide with +SHRA and isolated TSRA possible. This activity will likely bring MVFR ceiling and visibility with some IFR conditions where the heavier activity occurs. Numerous showers are expected to continue through the evening and into tonight.
Winds will remain relatively light through the forecast period.
AIRMET SIERRA remains in effect above 2000 feet for Maui and Lanai due to tempo mountain obscuration from clouds and showers.

Marine

Light winds are here to stay for most areas through the week as a cold front moves into the area, stalls, and diminishes into a trough by midweek. Background flow will remain out of the southeast direction over the eastern end of the state and variable around or near the boundary as it moves into the western end. Local winds, however, could become locally gusty in and around heavy showers/storms that develop over the next couple of days. Expect the light winds to persist into the second half of the week as a second front approaches and moves into the region by next weekend.
Surf along north facing shores will trend up by this afternoon as a reinforcing north-northwest pulse arrives. The observations at the offshore buoys northwest of Kauai reflected this uptick centered around the 11 second band around midnight. This source will gradually ease Monday through Wednesday as the swell direction shifts out of the north-northeast and lowers. Surf will continue to lower through the second half of the week and into next weekend.
Surf along east facing shores may trend up slightly Tuesday through midweek as the north-northwest swell shifts out of the north- northeast. Otherwise, the small trend will continue due to a combo of light winds locally and limited upstream fetch.

HFO Watches/Warnings/Advisories

Flood Watch through late tonight for all Hawaii islands,

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Data Courtesy of NOAA.gov