Photo Credit: James Grenz

Hilo

Today: Showers likely. Mostly cloudy, with a high near 80. West southwest wind around 5 mph becoming calm. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely, then occasional showers and possibly a thunderstorm after 7pm. Some of the storms could produce heavy rainfall. Low around 65. South southeast wind around 8 mph becoming west southwest after midnight. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Friday: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 80. West southwest wind around 9 mph becoming east southeast in the morning. 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, mainly after noon. Mostly cloudy, with a high near 83. Calm wind becoming west 5 to 8 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 65. Calm wind becoming east northeast around 6 mph after midnight. Chance of precipitation is 40%. 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 83. East northeast wind around 6 mph becoming light and variable in the afternoon. Chance of precipitation is 50%. New rainfall amounts between a half and three quarters of an inch possible.

Waimea

Today: Showers likely, mainly after 1pm. Mostly cloudy, with a high near 74. Breezy, with a northeast wind 17 to 20 mph, with gusts as high as 28 mph. Chance of precipitation is 60%. New precipitation amounts between a quarter and half of an inch possible.

Tonight: Showers likely, with thunderstorms also possible after 7pm. Some of the storms could produce heavy rainfall. Cloudy, with a low around 54. East southeast wind 5 to 8 mph. Chance of precipitation is 70%. New rainfall amounts between 1 and 2 inches possible.

Friday: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Cloudy, with a high near 74. East wind 5 to 10 mph. Chance of precipitation is 70%. New rainfall amounts between 1 and 2 inches possible.

Kohala

Today: Showers likely. Mostly cloudy, with a high near 67. Windy, with an east wind 21 to 26 mph decreasing to 10 to 15 mph in the afternoon. Winds could gust as high as 38 mph. Chance of precipitation is 70%. 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 46. East southeast wind 5 to 10 mph becoming light southeast in the evening. Chance of precipitation is 80%. 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 67. Light southeast wind becoming east 8 to 13 mph in the morning. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

South Big Island

Today: Scattered showers, mainly after noon. Mostly cloudy, with a high near 83. Breezy, with an east wind 17 to 22 mph, with gusts as high as 28 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 71. Breezy, with an east northeast wind around 18 mph, with gusts as high as 23 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. Mostly cloudy, with a high near 83. Breezy, with an east wind 17 to 22 mph, with gusts as high as 28 mph. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Puna

Today: Showers likely. Mostly cloudy, with a high near 78. Northwest wind 9 to 13 mph becoming east southeast in the afternoon. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Low around 63. East southeast wind around 9 mph becoming northwest in the evening. Chance of precipitation is 90%. New rainfall amounts between three quarters and one inch possible.

Friday: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 78. Northwest wind 8 to 11 mph becoming east in the morning. Chance of precipitation is 90%. New rainfall amounts between three quarters and one inch possible.

Waikoloa

Today: Scattered showers, mainly after 1pm. Mostly cloudy, with a high near 80. Breezy, with a north northeast wind 11 to 18 mph, with gusts as high as 25 mph. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter 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 64. Light east southeast wind. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Friday: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 80. Light and variable wind. Chance of precipitation is 50%. New rainfall amounts between a half and three quarters of an inch possible.

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