Photo Credit: Tyler Rooke

West Side

Today: Scattered showers, mainly after noon. Mostly cloudy, with a high near 84. Breezy, with an east wind 10 to 15 mph becoming light and variable. Winds could gust as high as 21 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 67. North northeast wind 7 to 9 mph. Chance of precipitation is 40%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Friday: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 84. North northeast wind 7 to 9 mph becoming southwest in the morning. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

South Side

Today: Showers likely after noon. Mostly cloudy, with a high near 84. Light and variable wind becoming east northeast 6 to 11 mph in the afternoon. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 66. East northeast wind around 11 mph. Chance of precipitation is 50%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Friday: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 84. East northeast wind around 10 mph becoming north northwest in the morning. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

North Shore

Today: Scattered showers. Mostly cloudy, with a high near 83. Windy, with an east wind 16 to 24 mph, with gusts as high as 34 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Cloudy, with a low around 66. Breezy, with an east wind 14 to 16 mph, with gusts as high as 22 mph. Chance of precipitation is 70%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Friday: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Cloudy, with a high near 83. Breezy, with an east northeast wind 14 to 16 mph, with gusts as high as 22 mph. Chance of precipitation is 70%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Central Maui

Today: Scattered showers, mainly after noon. Mostly cloudy, with a high near 83. Breezy, with an east northeast wind 13 to 21 mph, with gusts as high as 29 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth 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 65. North northeast wind 10 to 13 mph. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Friday: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 83. North northeast wind 10 to 14 mph, with gusts as high as 18 mph. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Upcountry

Today: Showers likely after 1pm. Mostly cloudy, with a high near 69. Calm wind becoming west 5 to 7 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Showers likely, with thunderstorms also possible after 7pm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 55. East wind 11 to 13 mph. Chance of precipitation is 60%. New rainfall amounts between three quarters and one inch possible.

Friday: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 69. South southeast wind 11 to 14 mph, with gusts as high as 18 mph. Chance of precipitation is 50%. New rainfall amounts between three quarters and one inch possible.

East Maui

Today: Showers likely, mainly after noon. Mostly cloudy, with a high near 81. Breezy, with an east southeast wind 7 to 16 mph, with gusts as high as 22 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Low around 63. Breezy, with an east southeast wind around 16 mph, with gusts as high as 22 mph. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible.

Friday: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 81. Breezy, with an east wind 14 to 16 mph, with gusts as high as 22 mph. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible.

Lanai City

Today: Showers likely, mainly after 1pm. Mostly cloudy, with a high near 73. East northeast wind 8 to 13 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Showers likely, with thunderstorms also possible after 7pm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 63. North northeast wind around 7 mph. Chance of precipitation is 70%. New rainfall amounts between a half and three quarters of an inch possible.

Friday: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 73. North northeast wind 6 to 10 mph becoming west southwest in the morning. Chance of precipitation is 50%. New rainfall amounts between a half and three quarters of an inch possible.

Kaunakakai

Today: Scattered showers after 1pm. Mostly cloudy, with a high near 82. East wind around 14 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.

Tonight: Scattered showers, with thunderstorms also possible after 7pm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 70. East wind around 14 mph, with gusts as high as 18 mph. Chance of precipitation is 40%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Friday: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 82. Breezy, with an east wind 13 to 18 mph, with gusts as high as 25 mph. Chance of precipitation is 50%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Detailed Forecast

Synopsis

Cloudy skies and increasing moisture associated with an upper disturbance and surface trough in the area will lead to increasing rainfall chances statewide today through Saturday. Heavy showers and a few storms will become a possibility through this time, which increases the threat for localized flash flooding. In addition to the potential for heavy rainfall, a wintry mix appears possible at the summits of the Big Island later today through Friday night. Conditions should gradually begin to improve and trend back toward a typical trade wind pattern over the weekend through early next week.

Discussion

Guidance remains persistent and continues to advertise a wet pattern unfolding over the state today through Saturday as an upper disturbance and surface trough influence the local weather. Some showers may become heavy and lead to localized flooding concerns where they become focused for any duration. In addition to the rainfall, a few thunderstorms will be possible as instability associated with an upper low increases and the trade wind inversion erodes. As the surface trough sets up near the western end of the state, low-level flow will veer out of the east-southeast direction and slightly weaken – likely giving way to a land and sea breeze regime over sheltered leeward and interior locations beginning this afternoon.
Despite the high sun angle over the islands in May, the one limiting factor to the flooding rain threat could be the canopy of mid-to-high clouds draped over the area limiting daytime heating and boundary layer instability over those shelter leeward areas through the afternoon hours. High-resolution rainfall guidance reflects this to some degree and shows the bulk of the rainfall accumulations setting up over windward and mountain locations with peak 48-hr totals reaching the 3-5 inch range.
For the summits of the Big Island, deep tropical moisture lifting northward into the area east of the upper low combined with freezing temperatures will likely translate to a wintry mix later today through Friday night. Conditions should gradually improve at the summits over the weekend.
Conditions should improve and trend back toward a typical trade wind pattern statewide over the weekend through early next week as drier air moves in and the upper disturbance lifts northward away from the state.

Aviation

Broken to overcast high clouds will prevail through the forecast period. Beneath these clouds, expect VFR conditions at the terminals to continue. Clouds and showers embedded in low level trade wind flow will interact with island terrain, causing brief periods of local MVFR conditions over windward slopes.
AIRMET Tango is currently posted for low level mechanical turbulence over and downwind of terrain on all islands. Winds are expected to diminish later today.

Marine

Strong high pressure located far north of the islands and its resultant pressure gradient directed back toward the state will generally produce moderate to fresh trade winds today. An upper level low moving into the area from the southwest, along with its associated broad western water surface trough, will weaken and slightly veer today’s east trades, especially over more leeward and west island waters. Little movement of this surface trough, along with the further strengthening of the northeast high, will create an overall fresh east trade flow over more eastern island windward waters yet maintain gentle to moderate southeasterlies over western island waters. The upper low may trigger periods of heavy rainfall and thunderstorms as it slowly meanders northeast toward the islands late tonight into Friday.
Surf along north and west facing shores will remain very small through Saturday. An area of strong to gale force winds along the southern periphery of a broad low near the west Aleutian Islands will be focused along a northwest great circle path directed at the islands. This small, short to medium period northwest swell is scheduled to arrive and boost north and west facing shore surf Saturday night into Sunday, hold on Monday and then drop off Tuesday. Surf along east facing shores should gradually trend up through the remainder of the week and weekend as fresh trades expand well upstream of the islands. South facing shore surf will remain small through Friday but will pick up a bit over the weekend with the arrival of the next very small, long period south swell. Expect this trend to hold next week with another small, long period south swell possibly arriving Tuesday and holding through the middle of next week.

HFO Watches/Warnings/Advisories

Flash Flood Watch from this evening through late Friday night for all Hawaii islands,
Winter Storm Watch from this evening through late Friday night for Big Island Summits.
Small Craft Advisory until 6 AM HST early this morning for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov