Photo Credit: Randy Alona Gallegos

West Side

Today: Mostly sunny. Isolated showers in the afternoon. Highs 78 to 85. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers after midnight. Lows 62 to 68. East winds up to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 78 to 85. East winds up to 10 mph. Chance of rain 40 percent.

South Side

Today: Mostly sunny. Highs around 84. Light winds becoming northwest around 10 mph in the afternoon.

Tonight: Mostly clear. Lows around 63. North winds up to 10 mph.

Thursday: Sunny. Isolated showers in the afternoon. Highs around 84. Northwest winds up to 10 mph. Chance of rain 20 percent.

North Shore

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 75 to 82 near the shore to around 64 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 60 to 66 near the shore to around 49 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny with showers likely. Highs 75 to 82 near the shore to around 62 near 5000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Central Maui

Today: Mostly sunny. Isolated showers in the afternoon. Highs 80 to 85. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 61 to 66. East winds up to 15 mph.

Thursday: Mostly sunny. Isolated showers in the afternoon. Highs 80 to 85. Northeast winds up to 15 mph. Chance of rain 20 percent.

Upcountry

Today: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 58 at the visitor center to around 55 at the summit. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy. Scattered showers after midnight. Lows around 42 at the visitor center to around 39 at the summit. Light winds becoming southeast up to 10 mph after midnight. Chance of rain 50 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 55 at the visitor center to around 52 at the summit. Light winds. Chance of rain 50 percent.

East Maui

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 75 to 82 near the shore to around 64 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 60 to 66 near the shore to around 49 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny with showers likely. Highs 75 to 82 near the shore to around 62 near 5000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Lanai City

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 71 to 78. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows around 63. Northeast winds up to 15 mph in the evening becoming light. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with showers likely in the afternoon. Highs 71 to 78. Light winds. Chance of rain 60 percent.

Kaunakakai

Today: Mostly sunny. Scattered showers in the afternoon. Highs 75 to 83. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows 60 to 69. East winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 20 percent.

Thursday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 75 to 83. East winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate trades will hold over the eastern islands through Thursday, while lighter trades and leeward land and sea breezes prevail over the western islands. Showers will favor windward slopes and coasts at night and interior and leeward areas each afternoon. More unsettled weather with thunderstorms and localized downpours appear in store as a disturbance aloft moves southeastward across the islands Friday and Saturday. Conditions should improve Sunday through early next week, as the most unsettled weather pushes east of the state.

Discussion

Currently at the surface, a cold front is located around 825 miles northwest of Kauai, while a 1032 mb high is centered 2200 miles northeast of Honolulu. The trade winds have eased to moderate levels overnight as the gradient has relaxed a bit. Infrared satellite imagery shows mostly cloudy conditions in most windward areas and partly cloudy skies in most leeward locales. Radar imagery shows scattered showers moving into windward slopes and coasts, with mostly dry conditions in leeward areas. Main forecast concern continues to revolve around the potential for some active and unsettled weather Friday and Saturday.
The cold front to the distant northwest will shift southeastward and closer to the islands during the next couple of days, eventually weakening into a broad trough over the islands on Friday. As a result, the trades will ease during the next few days. Moderate trade winds will hold over the eastern islands today and Thursday, while lighter trades over the western end of the state allow for land and sea breeze development in leeward areas. The trades ease further on Friday, allowing for sea breeze development statewide. The broad trough then appears to gradually dampen out over the weekend, which could allow some light to moderate trade winds to build back over the islands. By early next week, a new approaching cold front will begin to shift the low level boundary layer flow around to the southeast, maintaining moderate easterly trades over the eastern islands, while land and sea breezes become more dominant over the western end of the state.
As for the remaining weather details, a hybrid trade wind pattern should prevail through Thursday. Showers will favor windward and mauka areas overnight and during the morning, then transition over to interior and leeward areas each afternoon into the early evening. As the boundary layer flow becomes light and variable Thursday night, most of the shower activity should remain offshore or close to the islands coasts.
The weather pattern becomes much more interesting Friday through Saturday as an upper level low swings southeastward across the island chain, with broad surface troughing holding over the state. Precipitable water values don't appear all that high, generally holding at or below 1.5 inches over the smaller islands, while reaching as high as 1.7 inches over southeastern sections of the Big Island. As a result, a widespread heavy rain threat doesn't appear all that high, although some downpours will be possible that could bring some minor flooding impacts. We will continue to monitor the latest model trends as the need for a Flood Watch is still not out of the question, particularly over Maui County and the Big Island.
The more concerning threat revolves around the potential for severe thunderstorms. Mid-level 700-500 mb lapse rates reach 7 to 7.5 C/KM as the upper level low pivots southeastward through the islands, while surface based CAPE values increase to between 1000 and 1500 J/KG, and 0-1 KM MUCAPE values reach as high as 2000 J/KG. This in combination with 0-6 KM Bulk Shear values of 25 to 40 knots could lead to some stronger thunderstorms capable of producing hail and strong gusty winds. The one element that seems to be holding back the potential for well organized convection is the lack of a significant surface trigger aside from sea breezes. Nevertheless, we will need to keep a close eye on how this pattern evolves during the next couple days.
The most unstable airmass slides east of the state Saturday night, which should bring a return of a hybrid trade wind pattern featuring windward and mauka showers at night and interior and leeward showers during the afternoon and early evening hours. This pattern appears to generally hold through early next week.

Aviation

Light to moderate trades are expected to persist through tomorrow. Bands of light showers will continue to favor windward and mauka areas, and be most active during the overnight hours. With the lighter flow, sea breezes will develop across wind- protected leeward areas, bringing an increase in interior clouds and isolated showers by the afternoon. Land breezes may also help to clear out cloud cover across leeward areas overnight. Brief MVFR conditions are to be expected in passing showers, otherwise VFR conditions will prevail statewide.
No AIRMETs are in effect at this time, nor are any expected to be needed today.

Marine

Moderate to fresh trade winds will weaken over the next several days as high pressure northeast of the state moves further away and a front approaches the islands from the northwest. The front will weaken into a trough over the islands Friday as wind speeds look to ease and become light to gentle Friday and Saturday with southeast flow over the eastern half and northeast to east flow over the western half of the state. Gentle to locally moderate east to southeast flow looks to trend into the early half of next week across the coastal waters. An upper level low will move across the island chain Friday through Saturday which will increase the chance for heavy showers and potential thunderstorms.
The current northwest swell will continue to decrease to tiny conditions through Thursday followed by a reinforcing short- period north northwest swell Friday into the weekend. Surf along south facing shores will remain steady through today. Forerunners from a larger and longer lived south- southwest swell are subject to arrive later this afternoon. Surf is trending below High Surf Advisory (HSA) criteria but if nearshore buoy observations come in above guidance, surf could reach HSA criteria when the swell peaks Thursday into Friday before declining into the weekend. Surf along east facing shores should remain small as winds remain light through the rest of the week.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov