Photo Credit: James Grenz

Hilo

Today: Frequent showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 73. South wind around 5 mph becoming light and variable in the afternoon. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Frequent showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Low around 62. Breezy, with an east southeast wind 10 to 17 mph, with gusts as high as 24 mph. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Wednesday: Frequent showers and possibly a thunderstorm. High near 76. South southeast wind 8 to 11 mph. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Kona

Today: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Widespread haze. Mostly cloudy, with a high near 78. West wind around 5 mph becoming calm in the afternoon. Chance of precipitation is 70%. New rainfall amounts between a half and three quarters of an inch possible.

Tonight: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Widespread haze. Mostly cloudy, with a low around 61. East southeast wind 5 to 9 mph becoming north after midnight. Chance of precipitation is 70%. New rainfall amounts between a half and three quarters of an inch possible.

Wednesday: Scattered showers and thunderstorms. Widespread haze. Partly sunny, with a high near 79. Northwest wind around 6 mph. Chance of precipitation is 30%. New rainfall amounts between a quarter and half of an inch possible.

Waimea

Today: Frequent showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 71. East northeast wind 6 to 8 mph. Chance of precipitation is 90%. New rainfall amounts between 1 and 2 inches possible.

Tonight: Frequent showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Low around 51. East wind 5 to 13 mph. Chance of precipitation is 90%. New rainfall amounts between 1 and 2 inches possible.

Wednesday: Scattered showers and thunderstorms. Partly sunny, with a high near 73. East wind around 6 mph becoming south southwest in the afternoon. Chance of precipitation is 50%. New rainfall amounts between three quarters and one inch possible.

Kohala

Today: Frequent showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 68. East northeast wind around 6 mph. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Frequent showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Low around 44. East southeast wind 5 to 13 mph becoming north northwest after midnight. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Wednesday: Scattered showers and thunderstorms, then showers likely and possibly a thunderstorm after noon. Partly sunny, with a high near 70. South southwest wind around 6 mph. Chance of precipitation is 70%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

South Big Island

Today: Frequent showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Widespread haze. High near 79. Breezy, with an east northeast wind 16 to 21 mph, with gusts as high as 26 mph. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Frequent showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Widespread haze. Low around 69. Breezy, with an east wind 17 to 20 mph, with gusts as high as 25 mph. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Wednesday: Showers likely and possibly a thunderstorm. Widespread haze. Mostly cloudy, with a high near 79. Breezy, with an east wind 18 to 21 mph, with gusts as high as 26 mph. Chance of precipitation is 70%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Puna

Today: Frequent showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 75. East northeast wind 3 to 5 mph. Chance of precipitation is 100%. New rainfall amounts between three quarters and one inch possible.

Tonight: Frequent showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Low around 61. Breezy, with an east southeast wind 10 to 16 mph, with gusts as high as 22 mph. Chance of precipitation is 100%. New rainfall amounts between three quarters and one inch possible.

Wednesday: Showers likely and possibly a thunderstorm. Mostly cloudy, with a high near 76. Southeast wind around 8 mph. Chance of precipitation is 70%. New rainfall amounts between three quarters and one inch possible.

Waikoloa

Today: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 75. North northeast wind around 5 mph. Chance of precipitation is 70%. New rainfall amounts between a half and three quarters of an inch possible.

Tonight: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 60. East southeast wind 5 to 11 mph. Chance of precipitation is 70%. New rainfall amounts between three quarters and one inch possible.

Wednesday: A 20 percent chance of showers and thunderstorms. Mostly sunny, with a high near 79. West wind around 6 mph.

Detailed Forecast

Synopsis

Widespread showers, some locally heavy, are expected through tonight as an upper level disturbance enhances deep moisture moving in from the east and south. Locally strong east to southeast winds will continue today, then diminish tonight and Wednesday as a trough develops near the islands. The trough will linger until the end of the week, keeping winds light, and maintaining the potential for showers. Strong high pressure building north of the islands will bring breezy, dry and cool northeast winds this weekend.

Discussion

A cut-off low aloft will persist just W of the islands for the next couple of days, supporting an unstable island atmosphere as abundant moisture streams in from the E and SE. Meanwhile, a surface high far NE of the islands, currently supporting breezy to locally strong E winds, will change little. Persistent deep convection in the area will lead to the development of a surface trough near the islands today, with this feature expected to develop into a surface low W of the islands by Wednesday.
While significant differences exist amongst the reliable model guidance regarding the initial evolution of a surface trough near the islands, there is general agreement that low-level moisture convergence will remain maximized over the islands into tonight, shifting N of the islands on Wednesday as the trough develops into a surface low, and moves to a position W of Kauai. A Flash Flood Watch will remain in effect through 6 AM HST Wednesday, and if latest guidance verifies, we may be able to allow it to expire at that time. Moisture occasionally pushing up over the Big Island Summits, where temperatures remain below freezing, supports an extension of a Winter Weather Advisory until 6 AM HST Wednesday.
The official forecast favors the ECMWF solution, which depicts a surface trough developing SW of the islands today, becoming a weak surface low W of Kauai on Wednesday. This is expected to lead to a reduction in the coverage and intensity of rainfall over the islands by Wednesday, with light to moderate SE winds developing. The low will linger NW of Kauai on Thursday and Friday, with associated convergence bands potentially affecting portions of the islands, but guidance once again is placing the bulk of the moisture N and NE of the islands, with light S to SE winds keeping a humid air mass in place. This could result in a land-sea breeze pattern, with reduced showers over land during the late night and early morning, and increased showers over land in the afternoon and evening, but confidence is low.
A significant drying and cooling trend is expected over the weekend, as a strong shortwave aloft dives in from the NW on Friday. This shortwave will finally kick out the persistent cut-off aloft near the islands, but may trigger a period of unsettled weather as it passes overhead Friday and Saturday. After that, a strong high building N of the islands is expected to bring strong NE trade winds, with long term guidance indicating dew points lowering into the 50s F.

Aviation

An area of enhanced moisture will continue to spread over the islands from the southeast through today, lingering into tonight. Widespread shower activity, heavy at times, will lead to MVFR ceilings and visibility, especially along windward sides of all islands and over elevated terrain. Isolated IFR conditions are possible in the heavier bands of showers, along with isolated thunderstorms.
Breezy easterly winds will continue to generate tempo moderate turbulence below 8000 feet over and immediately west of mountains. AIRMET Tango remains in effect for this through at least tonight. Winds are expected to trend down slightly through tomorrow night.
AIRMET SIERRA remains in effect above 2000 feet for north thru east facing slopes of the Big Island, Molokai, and Oahu due to mountain obscuration from clouds and showers. North through east sections of Maui and Kauai are currently under tempo IFR conditions due to heavy showers, though Maui may be scaled back to mountain obscuration (MVFR) soon, as showers are beginning to abate there somewhat.

Marine

Strong high pressure centered far northeast of the state is producing fresh to strong trade winds across and upstream of the region. Strong trade winds will continue a Small Craft Advisory (SCA) that is in effect for all local waters through 6 AM HST Wednesday. While mid to late week trades will be on the decline, rough seas will take a little longer to dampen out. An upper level trough and associated surface trough will not only maintain high chances for frequent showers, some locally heavy, and periodic thunderstorms, it will also disrupt the trade flow pattern. The location of the surface trough will determine the magnitude and direction of this week’s coastal and offshore winds. If the trough does pass across the chain, then expect more variable winds and an overall weakening to mid to late week trades. A cold front passing over the waters this weekend will produce strong northeasterlies in its wake.
A High Surf Advisory (HSA) is in effect today for the east-facing shores of Kauai, Oahu, Molokai, Maui and the Big Island to account for the continued greater than 8 foot surf that will impact most eastern exposures. East-facing surf heights will remain elevated due to a combination of trade wind wave and eastern swell along with a small north swell wrap around northeastern shorelines. Surf heights along north and east-facing shorelines will remain uncertain due to a surface trough of low pressure laying across the islands. The location of this trough will disrupt the general large scale fresh to strong trade flow generated by the large scale pressure gradient from high pressure northeast of the chain. Low, moderate period overlapping predominant north swells will cause surf heights along north and west-facing shores to remain well below winter averages through the week. Strong north winds setting up behind a passing late week eastern Pacific cold front will follow a great circle path directed toward the state. This will generate a long fetch region that may allow large, long period north northeast swells to propagate into the islands this weekend. These swells could produce XL surf along north and east-facing shores over the weekend. Very small, lower period south southwest swells will continue to create small surf along south-facing shores.

HFO Watches/Warnings/Advisories

Flash Flood Watch through late tonight for all islands.
High Surf Advisory until 6 PM HST this evening for East facing shores of Kauai Oahu Molokai Maui and the Big Island.
Winter Weather Advisory until 6 AM HST Wednesday for Big Island Summits.
Small Craft Advisory until 6 AM HST Wednesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov