Hilo

Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 61 to 69 near the shore to 53 to 58 at 4000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Mostly cloudy. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 80 near the shore to around 69 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows 62 to 70 near the shore to 53 to 58 at 4000 feet. Light winds. Chance of rain 30 percent.

Kona

Tonight: Mostly cloudy. Isolated showers and thunderstorms in the evening. Locally heavy rainfall possible in the evening. Lows around 72 near the shore to 51 to 56 near 5000 feet. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 81 to 86 near the shore to around 67 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy. Lows 69 to 74 near the shore to 50 to 55 near 5000 feet. Light winds.

Waimea

Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 62 to 71 near the shore to 54 to 63 near 3000 feet. East winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible in the afternoon. Highs around 79 near the shore to 70 to 75 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy. Isolated showers in the evening. Lows 63 to 72 near the shore to 55 to 63 near 3000 feet. Light winds. Chance of rain 20 percent.

Kohala

Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 62 to 71 near the shore to 54 to 63 near 3000 feet. East winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible in the afternoon. Highs around 79 near the shore to 70 to 75 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy. Isolated showers in the evening. Lows 63 to 72 near the shore to 55 to 63 near 3000 feet. Light winds. Chance of rain 20 percent.

South Big Island

Tonight: Mostly cloudy. Isolated showers and thunderstorms in the evening. Lows around 74 near the shore to around 56 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 84 near the shore to around 67 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy. Isolated showers in the evening. Lows around 74 near the shore to around 56 near 5000 feet. Light winds. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 61 to 69 near the shore to 53 to 58 at 4000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Mostly cloudy. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 80 near the shore to around 69 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows 62 to 70 near the shore to 53 to 58 at 4000 feet. Light winds. Chance of rain 30 percent.

Waikoloa

Tonight: Mostly cloudy with isolated showers and thunderstorms in the evening, then partly cloudy after midnight. Locally heavy rainfall possible in the evening. Lows around 73 near the shore to around 55 above 4000 feet. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny in the morning, then partly sunny with scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 83 near the shore to 64 to 70 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy. Lows around 73 near the shore to 52 to 57 above 4000 feet. Light winds.

Detailed Forecast

Synopsis

An upper level trough passing through the Hawaii region on Monday will keep high and middle level clouds over the islands with brief showers and chances for a few thunderstorms. A series of low pressure systems developing northwest to north of the islands will weaken the ridge north of the state, producing weak southeasterly wind flow through Wednesday. The ridge builds back in north of the state by Thursday, allowing moderate easterly trade winds to return lasting through the upcoming weekend.

Short term update

The satellite imagery this evening shows a large Mesoscale Convective System (MCS) with frequent thunderstorms developing along a surface trough roughly 200 miles northwest of Kauai. While chances for showers and a few thunderstorms remain in the short term forecast through Monday morning as the upper trough passes over the western islands, the bulk of these heavy showers and thunderstorms associated with the MCS will likely track north of Kauai. However, the latest extrapolation track of this system approaches Kauai by early Monday morning around sunrise. The current intensity of this system should also weaken over time. We will continue to closely monitor this feature on satellite for any changes over the next several hours.

Previous discussion

Issued at 509 PM HST Sun Apr 19 2026 A surface trough, and an associated shortwave upper level trough are found a few hundred miles northwest of Kauai this afternoon. The shortwave is helping to trigger thunderstorms between 200 and 400 miles northwest of Kauai. As the shortwave swings to the east over the next day, thunderstorm activity will move with it. The GFS and ECMWF global models are in general agreement with the timing of these feature, however the GFS is stronger with the divergence associated with the upper level feature. Thunderstorm probabilities with the National Blend of Models (NBM), and climatological based thunderstorm probabilities with both the GFS and ECMWF keep the bulk of the instability to the north of the islands, but enough of it sinking southward tonight that its possible for some thunderstorms to make it into the islands. While the highest chance for thunderstorms will be over/near Kauai and Oahu, upslope thunderstorms on the Big Island are also possible. Have made some adjustments to the thunderstorm areas based on the latest guidance from the NBM, GFS and ECMWF.
The surface trough is expected to move over the islands behind the shortwave feature, and will lead to lighter winds Tuesday and Wednesday. Under this lighter wind regime, we are likely to see some showers develop over interior areas of the islands during the afternoon. Trade winds are expected to return to the islands Thursday, with more typical trade winds showers riding in on the trades by the weekend. Little change has been made to the PoPs and associated forecast fields from Wednesday onwards.

Aviation

Issued at 509 PM HST Sun Apr 19 2026 A light easterly background trade wind flow remains over the state today. The light winds have allowed some land and sea breezes to develop over terrain sheltered areas. Expect these winds to remain light and veer more ESE starting tomorrow. Showers remain possible for windward and mountain areas, and over island interiors during afternoon hours through tomorrow. An upper level disturbance moving eastward through the state combined with the light winds at the surface could increase afternoon shower coverage statewide tomorrow. MVFR conditions should be expected within showers, and IFR conditions are possible within heavier isolated downpours. VFR will occur elsewhere.
No AIRMETs are currently in effect.

Marine

Issued at 509 PM HST Sun Apr 19 2026 A trough of low pressure passing northwest of the state will act to weaken and veer winds east southeasterly through mid-week across the local waters. Light flow should allow for afternoon sea breeze development near the shores. As conditions become increasingly unstable aloft, isolated thunderstorms will be possible tonight into Monday over the waters surrounding Kauai and Oahu. By Thursday, high pressure ridging builds back in north of the state with fresh northeasterly trade winds returning to the region lasting through next weekend.
Swell and surf will remain small along all shores through late Monday.
A small, medium period, northwest swell will move across the waters Monday night and continue through Wednesday. Another small, long period, west northwest swell will enter the waters Wednesday night and provide a slight bump up for surf along west and northwest facing shores. A moderate, medium to long period, northeast swell arrives on Tuesday and peaks on Wednesday, bringing moderate surf to north- facing shores, before slowly declining through the end of the week.
Surf will remain small along south facing shores through the period. Surf heights along east facing shores also remain small due to weaker trade winds until the arrival of the aforementioned moderate, medium to long period, northeast swell building into the Hawaii region from Tuesday through Thursday.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov