Photo Credit: James Grenz

Hilo

Today: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 76. South southeast wind around 9 mph. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Occasional showers and possibly a thunderstorm, mainly before 1am, then scattered showers and thunderstorms after 1am. Some of the storms could produce heavy rainfall. Low around 63. South wind 5 to 8 mph. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Thursday: Scattered showers and thunderstorms, then showers likely after 7am. Some of the storms could produce heavy rainfall. Partly sunny, with a high near 78. Southeast wind 5 to 8 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Kona

Today: Scattered showers and thunderstorms after noon. Some of the storms could produce heavy rainfall. Widespread haze. Increasing clouds, with a high near 79. West northwest wind around 6 mph. Chance of precipitation is 30%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: A 20 percent chance of showers and thunderstorms. Some of the storms could produce heavy rainfall. Widespread haze. Mostly cloudy, with a low around 61. Northwest wind around 6 mph.

Thursday: Scattered showers after noon. Widespread haze. Mostly sunny, with a high near 79. West northwest wind 3 to 5 mph. Chance of precipitation is 40%. New precipitation amounts between a tenth and quarter of an inch possible.

Waimea

Today: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Partly sunny, with a high near 73. West wind around 6 mph. Chance of precipitation is 50%. New rainfall amounts between 1 and 2 inches possible.

Tonight: Scattered showers and thunderstorms, mainly before 7pm. Some of the storms could produce heavy rainfall. Partly cloudy, with a low around 52. West wind around 6 mph becoming south in the evening. Chance of precipitation is 50%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Thursday: A slight chance of showers and thunderstorms, then showers likely after 7am. Some of the storms could produce heavy rainfall. Partly sunny, with a high near 74. West southwest wind around 5 mph becoming light and variable in the afternoon. Chance of precipitation is 60%. New precipitation amounts between a quarter and half of an inch possible.

Kohala

Today: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 70. West 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.

Tonight: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 45. East southeast wind around 6 mph becoming west southwest after midnight. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Thursday: Occasional showers, mainly after noon. High near 70. North wind around 5 mph. Chance of precipitation is 80%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Widespread haze. Partly sunny, with a high near 79. Breezy, with an east wind 14 to 16 mph, with gusts as high as 21 mph. Chance of precipitation is 50%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Widespread haze. Mostly cloudy, with a low around 69. East northeast wind 11 to 14 mph. Chance of precipitation is 50%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Thursday: Scattered showers. Widespread haze. Partly sunny, with a high near 79. Breezy, with an east northeast wind 13 to 15 mph, with gusts as high as 18 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Puna

Today: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 76. South wind 10 to 13 mph. Chance of precipitation is 90%. New rainfall amounts between 1 and 2 inches possible.

Tonight: Occasional showers and possibly a thunderstorm before midnight, then scattered showers and thunderstorms after midnight. Some of the storms could produce heavy rainfall. Low around 61. South wind around 8 mph. Chance of precipitation is 80%. New rainfall amounts between three quarters and one inch possible.

Thursday: Occasional showers, mainly after noon. High near 76. East southeast wind around 7 mph. Chance of precipitation is 80%. New precipitation amounts between a half and three quarters of an inch possible.

Waikoloa

Today: A 20 percent chance of showers and thunderstorms after noon. Some of the storms could produce heavy rainfall. Mostly sunny, with a high near 79. West wind around 6 mph.

Tonight: A 20 percent chance of showers and thunderstorms. Some of the storms could produce heavy rainfall. Partly cloudy, with a low around 61. South southeast wind around 6 mph.

Thursday: Isolated showers. Mostly sunny, with a high near 80. Northwest wind 3 to 5 mph. Chance of precipitation is 20%.

Detailed Forecast

Synopsis

Widespread showers, some locally heavy, are expected statewide through today as a slow-moving low pressure system lingers west of Kauai. With the low remaining nearby for the next couple of days, light south winds will prevail, and the potential for showers will remain elevated. Wet weather may linger into next weekend.

Discussion

A cut-off low aloft will persist just W of the islands for the next couple of days. Although a pretty strong surface high sits NNE of the islands, the development of an associated surface low just W of the islands has loosened the gradient, leading to lighter winds that have turned to the SE and S. Heavy showers and strong thunderstorms are developing E of the low over Kauai County and adjacent waters, while scattered heavy showers are noted elsewhere. However, showers have been especially persistent and heavy over the Big Island’s Puna District for the last several hours, as the moist and unstable S flow interacts with the terrain.
Models agree that low-level moisture convergence will remain maximized over the islands today, gradually shifting N of the islands by Thursday/Friday as the surface low lingers W of Kauai, then maybe moves to a position N of the islands. A Flash Flood Watch (FFA) remains in effect through 6 PM HST today, especially given how saturated most areas are. Moisture occasionally pushing up over the Big Island Summits, where temperatures remain below freezing, supports the continuation of a Winter Weather Advisory until 6 PM HST Wednesday.
With the low expected to linger, associated convergence bands may continue to periodically affect 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. Difficult to know if the FFA will need to be extended, and if so, for which islands. The light winds 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 weakened version of the low may move over the islands on Friday, bringing the potential for another period of widespread increased rainfall.
A significant drying and cooling trend is possible late in the weekend, per ECMWF, but GFS keeps a wet weather pattern in place, so confidence is severely reduced.

Aviation

Organized heavy showers and MVFR cigs/vsby are ongoing over Kauai and portions of the Big Island with scattered activity in between. Isolated to scattered thunderstorms are also ongoing over Kauai and adjacent waters. This general pattern is forecast to persist through today as the resident upper low maintains some degree of lift over Kauai and developing southeast flow focuses showers over Big Island from roughly Cape Kumukahi to South Cape. Less organized showers, isolated thunderstorms, and periods of MVFR will be possible at times for all locations.
AIRMET Sierra remains in effect for Kauai, Windward Molokai, and portions of Big Island. Further expansion to Oahu and Molokai may be required during the morning.
AIRMET Tango for lee turbulence has been cancelled as winds continue to weaken and veer to southeasterly.

Marine

The surface low over the western offshore waters has disrupted trade flow over the Hawaiian Islands. Weakened trades will veer more southeast and trend more variable the next few days. The upper level low sitting over the region will be the impetus for continued periods of showers and thunderstorms. The jury is still out on what will become of weekend winds. An approaching cold front/trough is forecast to reach the offshore waters by early Saturday. High pressure north of the chain will be moving more eastward than southeastward and this may not provide the push needed to have the front passing east of the Big Island. If the front does reach our eastern waters this weekend, strong northeast winds will occur in its wake. If the front stalls north of the state, expect generally remain light to moderate easterlies.
Rough seas has extended a truncated Small Craft Advisory for the Oahu windward waters eastward, including the Alenuihaha Channel and the Big Island’s southeast waters through 6 PM HST today. Recent satellite derived winds depict an abundance of fresh to strong easterly trade winds occurring over and upstream of the chain. These winds, along with a lingering small, low period north swell wrap, will maintain elevated, near-advisory level surf along many full eastern exposures throughout the day. A surface low over the west waters will disrupt island trade flow from today through Friday and this will ultimately lower east-facing shoreline surf the next couple of days. North swells will continue to fade through Thursday afternoon with only small north and west-facing shore surf through Friday. Larger, longer period northeast swells arriving this weekend will likely boost surf heights along north and east-facing shorelines back up to high surf advisory levels. Very small, background southwest to south swells will keep surf small along most southern-facing shores.

HFO Watches/Warnings/Advisories

Flash Flood Watch through this afternoon for all islands.
Winter Weather Advisory until 6 PM HST this evening for Big Island Summits.
Small Craft Advisory until 6 PM HST this evening for Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Alenuihaha Channel, Big Island Windward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov