Photo Credit: Tyler Rooke

West Side

Today: Mostly cloudy. Slight chance of thunderstorms and isolated showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs 76 to 82. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 64. Light winds. Chance of rain 60 percent.

Monday: Partly sunny with scattered showers. Highs 76 to 82. Light winds. Chance of rain 30 percent.

South Side

Today: Mostly cloudy. Slight chance of thunderstorms and isolated showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs around 82. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 63. Light winds. Chance of rain 60 percent.

Monday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 82. Light winds. Chance of rain 30 percent.

North Shore

Today: Mostly cloudy. Scattered showers and slight chance of thunderstorms in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 74 to 79 near the shore to around 58 near 5000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 60 to 66 near the shore to around 47 near 5000 feet. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 60 percent.

Monday: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 74 to 79 near the shore to around 59 near 5000 feet. Light winds. Chance of rain 50 percent.

Central Maui

Today: Mostly cloudy. Slight chance of thunderstorms and isolated showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs 78 to 83. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 61 to 66. Light winds. Chance of rain 60 percent.

Monday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 78 to 83. Light winds. Chance of rain 30 percent.

Upcountry

Today: Mostly cloudy. Slight chance of thunderstorms and isolated showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 52 at the visitor center to around 47 at the summit. South winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 43 at the visitor center to around 37 at the summit. South winds up to 10 mph. Chance of rain 60 percent.

Monday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 54 at the visitor center to around 49 at the summit. South winds up to 10 mph. Chance of rain 50 percent.

East Maui

Today: Mostly cloudy. Scattered showers and slight chance of thunderstorms in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 74 to 79 near the shore to around 58 near 5000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 60 to 66 near the shore to around 47 near 5000 feet. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 60 percent.

Monday: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 74 to 79 near the shore to around 59 near 5000 feet. Light winds. Chance of rain 50 percent.

Lanai City

Today: Mostly cloudy. Slight chance of thunderstorms and isolated showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 71 to 78. Light winds. Chance of rain 60 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 64. Light winds. Chance of rain 60 percent.

Monday: Mostly cloudy with scattered showers. Highs 72 to 79. Light winds. Chance of rain 50 percent.

Kaunakakai

Today: Mostly cloudy. Slight chance of thunderstorms and isolated showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 71 to 81. Light winds. Chance of rain 60 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 54 to 66. Light winds. Chance of rain 60 percent.

Monday: Partly sunny with scattered showers. Highs 71 to 81. Light winds. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A low northwest of the islands will move away from the area, but a moist and unstable southerly wind flow will remain in place through Monday. There will be a chance of thunderstorms statewide through tonight, but heavy rainfall will be most likely over Oahu and Kauai County. A gradual drying trend is expected to begin Monday, with winds becoming light. The light winds will combine with a stable island atmosphere by midweek, with much fewer showers expected.

Discussion

Currently at the surface, a surface low is located to the distant northwest, with a weakening cold front extending southward from the low to a location around 300 miles west of Kauai. Meanwhile, a 1025 mb high is centered around 2000 miles east-northeast of the Big Island. Closer to home, a north to south oriented trough of low pressure is located around 50 miles west of the Garden Isle, with widespread convection along and to the east of this feature. The boundary layer wind fields are generally south and southeast at moderate speeds, creating a confluent flow over the island chain. Infrared satellite imagery shows mostly cloudy conditions over Kauai and Oahu, with partly cloudy skies over the other islands. Radar imagery shows widespread showers and a few thunderstorms over Kauai and Oahu, with isolated showers over the remainder of the state. Main short term concern revolves around rainfall trends during the next few days.
High pressure will remain centered to the distant east-northeast through early next week, while the weakening front several hundred miles west of Kauai dissipates. Moderate south to southeasterly winds are expected today, before easing to light levels tonight through Monday night. A new cold front approaching from the northwest will shift winds around to the south and southwest on Tuesday and Tuesday night, with winds becoming light and variable on Wednesday as the front stalls out and dissipates a few hundred miles northwest of Kauai. Light trades may briefly return Wednesday night and Thursday as a weak and fast moving high slides by to the north of the state, but will likely be overpowered in many areas by overnight land breezes and daytime sea breezes, particularly in leeward areas. Winds appear to remain light Thursday night, but could pick up slightly out of the west and southwest Friday as a weakening front approaches from the northwest. Overall, light winds are expected through the vast majority of the next 7 days.
As for the remaining weather details, confluent southerly flow and troughing aloft will keep unsettled conditions in place today and tonight. Numerous showers and a few thunderstorms are expected today over Kauai and Oahu, and as a result the Flood Watch has been extended through 6 PM this evening. Scattered to numerous showers and a thunderstorm or two are also expected over Maui County and the Big Island this afternoon, with locally heavy rainfall possible here as well. The flood threat over Maui County and the Big Island doesn't appear as great, so will leave these areas out of the Flood Watch.
The airmass will begin to slowly dry and stabilize during the first half of the week, as the deepest moisture lifts out to the northeast along with troughing aloft. Precipitable water values fall below 1.5 inches Monday morning and drop to around 1.2 inches or less by late Wednesday. The airmass appears to dry out further Thursday and Friday with precipitable water values dropping below 1 inch in many areas. As a result, we should see shower coverage and intensity gradually diminish through the week, with mostly dry conditions expected across the majority of the state for Thursday and Friday. A predominantly land and sea breeze pattern is expected for much of next week, which favors interior showers each afternoon and a few showers near the coast each night.

Aviation

An upper level low just west of Kauai will keep periods of wet weather with isolated thunderstorms in the forecast through this evening. The highest chances for MVFR/IFR conditions will remain over the islands of Kauai, Oahu and Molokai. Enough mid level clouds will linger over Kauai and Oahu to produce light icing conditions.
AIRMET SIERRA remains in effect for tempo mountain obscurations over Kauai and Oahu.
AIRMET Tango remains in effect for tempo moderate turbulence for all islands between FL200 and FL300.

Marine

Light to moderate SE to S winds today will weaken on Monday as a surface ridge builds over the area from the ENE, with light and variable winds expected for most of next week as the ridge remains close to the islands. A brief and short-lived period of trade winds is possible around midweek. A mid-level ridge building over the area will support a stable island atmosphere, with much fewer showers by the middle of the week.
Several WNW to NW swells are expected in the coming week. The first relatively small swell will be peaking today before diminishing Monday. The second swell is expected to build Tuesday into Wednesday, with resultant surf heights along exposed N and W facing shores easily reaching High Surf Advisory criteria as the long-period (open ocean) swell peaks near 10 feet into Thursday. The third swell could bring even larger surf next weekend as an extended fetch develops to the NW of the islands, with even more large surf potential in the extended forecast. A strong, slow- moving low in the Bering Sea will also send a long- to medium- period N swell through the area from Tuesday into Thursday. While winds will remain below Small Craft Advisory (SCA) criteria through the period, combined seas greater than 10 feet will likely require a SCA Wednesday and Thursday, and potentially again next weekend.

HFO Watches/Warnings/Advisories

Flood Watch through 6 PM this evening of Niihau, Kauai and Oahu.

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Data Courtesy of NOAA.gov