Photo Credit: James Grenz

Hilo

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 83 near the shore to 64 to 71 at 4000 feet. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Locally heavy rainfall possible early in the morning. Lows 64 to 71 near the shore to 55 to 61 at 4000 feet. Light winds becoming south around 10 mph after midnight. Chance of rain 50 percent.

Sunday: Partly sunny. Scattered showers and isolated thunderstorms in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 76 to 82 near the shore to 63 to 68 at 4000 feet. Southeast winds 10 to 15 mph decreasing to up to 10 mph in the afternoon. Chance of rain 70 percent.

Kona

Today: Mostly sunny. Isolated showers in the afternoon. Highs 81 to 86 near the shore to around 68 near 5000 feet. Light winds becoming west around 10 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers and thunderstorms until early morning, then scattered showers and isolated thunderstorms early in the morning. Locally heavy rainfall possible after midnight. Lows 70 to 75 near the shore to 50 to 57 near 5000 feet. Light winds becoming northeast around 10 mph after midnight. Chance of rain 50 percent.

Sunday: Mostly sunny with scattered showers and isolated thunderstorms in the morning, then mostly cloudy with showers likely and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 82 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 70 percent.

Waimea

Today: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 65 to 83. Light winds. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers and thunderstorms. Locally heavy rainfall possible after midnight. Lows 63 to 69 near the shore to 56 to 63 near 3000 feet. Light winds becoming southeast around 10 mph after midnight. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers and thunderstorms in the morning, then mostly cloudy with showers likely and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 63 to 81. Southeast winds around 10 mph in the morning becoming light. Chance of rain 70 percent.

Kohala

Today: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 65 to 83. Light winds. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers and thunderstorms. Locally heavy rainfall possible after midnight. Lows 63 to 69 near the shore to 56 to 63 near 3000 feet. Light winds becoming southeast around 10 mph after midnight. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers and thunderstorms in the morning, then mostly cloudy with showers likely and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 63 to 81. Southeast winds around 10 mph in the morning becoming light. Chance of rain 70 percent.

South Big Island

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 82 near the shore to around 66 near 5000 feet. East winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Locally heavy rainfall possible early in the morning. Lows around 72 near the shore to around 52 near 5000 feet. East winds around 10 mph. Chance of rain 50 percent.

Sunday: Mostly cloudy. Scattered showers and isolated thunderstorms in the morning, then showers likely and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 81 near the shore to around 64 near 5000 feet. East winds 10 to 15 mph in the morning becoming light. Chance of rain 70 percent.

Puna

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 83 near the shore to 64 to 71 at 4000 feet. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Locally heavy rainfall possible early in the morning. Lows 64 to 71 near the shore to 55 to 61 at 4000 feet. Light winds becoming south around 10 mph after midnight. Chance of rain 50 percent.

Sunday: Partly sunny. Scattered showers and isolated thunderstorms in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 76 to 82 near the shore to 63 to 68 at 4000 feet. Southeast winds 10 to 15 mph decreasing to up to 10 mph in the afternoon. Chance of rain 70 percent.

Waikoloa

Today: Sunny. Isolated showers in the afternoon. Highs 80 to 87 near the shore to 66 to 71 above 4000 feet. Light winds becoming northwest up to 10 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers and thunderstorms after midnight. Locally heavy rainfall possible after midnight. Lows around 73 near the shore to 51 to 57 above 4000 feet. Light winds. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers and thunderstorms in the morning, then mostly cloudy with showers likely and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 79 to 85 near the shore to 63 to 69 above 4000 feet. East winds around 10 mph in the morning becoming light. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Expect light winds to become southerly as a front approaches the area over the next few days. Showers will increase by Sunday as the front reaches the islands and begins to weaken into a trough. This trough will linger over or near the state into midweek, keeping winds rather light. Chances for rainfall will be greater east of the trough.

Discussion

A front about 350 miles northwest of the main Hawaiian islands has weakened the subtropical ridge, causing winds across local waters to decrease and veer noticeably to southeasterlies. This front will affect our weather into midweek as it reaches Kauai on Sunday and weakens. Expect light winds to veer to southerlies as the front continues to approach. Showers will increase beginning late tonight. Expect rather dry conditions to persist until then.
A surface high far northeast of the state has an associated ridge extending southwestward toward the islands. Veering low level flow has begun to increase airmass moisture, with PW values rising into the 1.15 to 1.30 inch range overnight. Noticeable inversions persist, with bases between 4800 feet and 5800 feet, capping deep convection this morning. Light low level flow has allowed development of land breezes, clearing skies of low clouds across the islands. However, radar shows showers beginning to increase offshore to the southwest of Kauai within the past few hours. Thickening high clouds are streaming northeastward across the state as flow aloft begins to adjust to a broad upper trough approaching from the northwest.
The weakening front is forecast to be near Kauai Sunday and Sunday night. Low level convergence within southerly flow may trigger development of shower bands ahead of the front. Kauai may see increased rainfall as the front arrives, while the other islands see increased showers from these convergence bands. Thunderstorms are possible tonight through Sunday night, but the greatest instability is expected to remain just north of the state. Locally heavy rainfall is possible both along the front and ahead of it within the prefrontal shower bands. However, widespread heavy rainfall is not expected. By Monday, the front is forecast to stall and weaken to a trough over the central islands.
Models show a gradual return to moderate trade flow by Thursday as the surface trough washes out and weak surface ridging builds back in from the east. Lingering moisture will be blown back westward as trade flow increases, hinting at drier conditions by the end of the work week.

Aviation

Wind flow will remain light with background southeasterlies over the eastern islands and south to southwesterlies background winds over the western half of the state today. Large scale wind speeds will remain light enough to allow local scale land and sea breezes to continue over each island through Sunday. A weakening cold frontal trough will produce increasing showers near Kauai today with tropical moisture adding instability and increasing showers near the Big Island.
A convergence band of clouds associated with the weakening cold front will move into the Kauai region by this evening, increasing shower activity with the potential for heavy showers and MVFR conditions. A tropical moisture plume moving northward into the Big Island this afternoon and evening will also produce periods of MVFR conditions with the potential for heavy rain and thunderstorms. Higher rainfall trends are expected to spread to all islands on Sunday.
AIRMET Tango is in effect for moderate upper level turbulence between FL250 and FL400 due to the subtropical jet over the island chain. The jet stream will strengthen later this weekend as it merges with the polar jet, likely keeping this AIRMET around through at least Sunday.

Marine

A cold front will be entering the northwestern offshore waters today. As the west upper trough and this associated surface front approach the western Hawaiian Islands this weekend, offshore and near coastal locally heavy rain and isolated thunderstorm chances will be on the rise the next few days. Gentle to moderate easterly winds (primarily over the windward waters) will veer more southerly as the front comes in proximity of the islands tonight. Moderate winds will swing northeasterly behind the boundary as it slowly moves into the central waters late Sunday. Breezes will remain light and variable as the stalling front transitions to a weak trough across the central islands Monday. A more typical trade wind pattern returns by Wednesday and will hold through the remainder of the week.
The ongoing moderate, medium period northwest swell is peaking surf along north and west facing shores this morning with a subtle decline expected from tonight into Sunday morning. On the heels of this swell will come another similar moderate size, medium period northwest swell that will be filling in through Sunday. This swell may push north and west shore surf to more seasonable heights Sunday and Monday but will fall well short of high surf advisory thresholds. The reasoning is that this reinforcing swell will originate from more local, short north fetch source region behind the aforementioned cold front entering the northwest offshore waters today. This northwest swell will transition more northerly on Monday as it subsides into Tuesday. Very small, long period south background energy will keep surf along south facing shores on the small side throughout the forecast period. Eastern shore chop will remain small the next several days due to this ongoing weak wind regime. Northern exposures along both south and east facing shores will experience higher surf from northwest swell energy wrap.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov