Hilo

Today: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 76. Calm wind becoming east southeast around 6 mph in the morning. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Low around 64. Northeast wind around 6 mph becoming calm after midnight. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Sunday: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 74. Light and variable wind becoming east northeast 5 to 10 mph in the afternoon. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible.

Kona

Today: Scattered showers, mainly after 1pm. Partly sunny, with a high near 78. Calm wind becoming west northwest 5 to 7 mph in the afternoon. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 62. Southwest wind around 6 mph becoming calm in the evening. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.

Sunday: Scattered showers, with thunderstorms also possible after 1pm. Partly sunny, with a high near 78. Calm wind becoming southwest around 6 mph in the afternoon. Chance of precipitation is 50%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Waimea

Today: Occasional showers, mainly before noon. High near 73. Breezy, with a northeast wind 15 to 21 mph, with gusts as high as 29 mph. Chance of precipitation is 80%. New precipitation amounts between a half and three quarters of an inch possible.

Tonight: Occasional showers. Low around 53. Breezy, with a northeast wind 17 to 21 mph, with gusts as high as 29 mph. Chance of precipitation is 80%. New precipitation amounts between three quarters and one inch possible.

Sunday: Showers likely, with thunderstorms also possible after noon. Partly sunny, with a high near 73. Windy, with a northeast wind 18 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 70%. New rainfall amounts between three quarters and one inch possible.

Kohala

Today: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 69. Windy, with an east wind around 29 mph, with gusts as high as 41 mph. Chance of precipitation is 80%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Low around 46. Very windy, with an east wind 29 to 31 mph, with gusts as high as 45 mph. Chance of precipitation is 90%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Sunday: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 69. Very windy, with an east northeast wind 28 to 31 mph, with gusts as high as 45 mph. Chance of precipitation is 80%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

South Big Island

Today: Scattered showers. Partly sunny, with a high near 78. Windy, with an east northeast wind 21 to 28 mph, with gusts as high as 36 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely and possibly a thunderstorm. Mostly cloudy, with a low around 70. Windy, with an east northeast wind 24 to 28 mph, with gusts as high as 36 mph. Chance of precipitation is 60%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Sunday: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 78. Windy, with an east northeast wind 24 to 28 mph, with gusts as high as 36 mph. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Puna

Today: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 75. Light north northwest wind becoming northeast 5 to 9 mph in the afternoon. Chance of precipitation is 90%. New rainfall amounts between 1 and 2 inches possible.

Tonight: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Low around 62. Northeast wind 6 to 9 mph becoming northwest after midnight. Chance of precipitation is 90%. New rainfall amounts between a half and three quarters of an inch possible.

Sunday: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 73. Breezy, with a north wind 5 to 10 mph becoming north northeast 11 to 16 mph in the afternoon. Winds could gust as high as 22 mph. Chance of precipitation is 90%. New rainfall amounts between 1 and 2 inches possible.

Waikoloa

Today: Scattered showers after noon. Mostly sunny, with a high near 79. Breezy, with a south wind 5 to 10 mph becoming east northeast 16 to 21 mph in the afternoon. Winds could gust as high as 29 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 62. Breezy, with an east wind 16 to 21 mph decreasing to 10 to 15 mph after midnight. Winds could gust as high as 29 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Sunday: Scattered showers and thunderstorms after noon. Mostly sunny, with a high near 79. Very windy, with an east northeast wind 26 to 31 mph decreasing to 13 to 18 mph. Winds could gust as high as 45 mph. Chance of precipitation is 30%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Detailed Forecast

Synopsis

Strong and gusty trade winds will continue into early next week, while a trough aloft keeps the island atmosphere unstable. Clouds and showers will focus over windward areas, with some occasional heavy downpours. Increasing moisture near Maui and the Big Island will bring a more widespread threat of heavy windward showers, and a slight chance of thunderstorms. Typical trade wind weather will continue through much of next week, with showers favoring windward and mauka areas and spreading into leeward communities from time to time.

Discussion

Currently at the surface, a 1041 mb high is centered around 1550 miles northeast of Honolulu, while another 1037 mb high is centered around 1450 miles northwest of Kauai. In between these two highs, a nearly stationary south-southwest to north-northeast oriented front is located around 850 miles northwest of the Garden Isle. The gradient over the local area remains rather tight early this morning, with breezy trade winds prevailing across the entire island chain. Infrared satellite imagery shows mostly cloudy to overcast skies in most windward areas, while clear to partly cloudy conditions prevail in most leeward locales. Radar imagery shows scattered to numerous showers moving into windward and mauka areas, with a few showers spreading into leeward communities from time to time. Main short term concerns revolve around the Flash Flood and Winter Weather headlines, as well as the trade wind trends through the weekend.
High pressure northeast of the state will settle southward and weaken during the next couple days, while the high northwest of the state builds eastward and strengthens to around 1044-46 mb by late Sunday and Sunday night due north of the island chain. This high will settle southward and weaken slightly early next week, followed by a new 1044 mb high building northwest of the state during the middle to latter part of next week. Overall, breezy to windy trades are expected to continue through the weekend and into early next week, with the trades peaking late Sunday through early Tuesday. Wind Advisories will likely be required once again for portions of the state during this time. The trades should ease a bit for the middle and latter part of next week, but will likely hold at moderate to breezy levels.
As for the remaining weather details, the island atmosphere will remain unstable through the weekend and into next week, due to the presence of a persistent trough aloft, and its associated cold pool. As a result, inversion heights will be pretty much eliminated, allowing for heavier showers to affect windward areas and sending showers into leeward communities more regularly as well. While these showers will be progressive and will not linger over any one area for a prolonged time, high-resolution and global model guidance continues to indicate the likelihood of repeated development over the windward slopes of Maui and the Big Island during the next couple days. This persistent rainfall is expected to lead to increasing ground saturation and rising levels in streams and rivers, with additional rainfall potentially resulting in flash flooding as the weekend progresses. As a result, a Flash Flood Watch (FFA) remains in effect for windward portions of Maui and the Big Island. An expansion of the FFA to windward portions of the other islands is not anticipated.
The cold temperatures aloft and deeper-than-normal moisture means that the Big Island Summits will receive periods of wintry weather, with the primary threats being freezing rain or drizzle leading to icy roadways, although snow showers will mix in as well. A Winter Weather Advisory remains in effect through Monday morning, and may need to be extended as the trough aloft lingers well into next week.

Aviation

Early this morning, shower activity along with MVFR level clouds and visibility have become more widespread along eastern sections of Maui and the Big Island. This trend is expected to continue throughout the day, with occasional heavy showers and even a few thunderstorms possible in these areas. AIRMET Sierra remains in effect for tempo mountain obscuration for Maui, but it is possible that this will need to be expanded to include the Big Island later this morning as showers and cloud cover continue to gradually increase. For the rest of the state, VFR conditions should prevail with showers favoring north through east sections of the islands.
Additionally, strong high pressure remains in place northeast of the main Hawaiian Islands. This will keep winds breezy to locally strong today, though they will not be quite as strong as the previous couple of days. AIRMET Tango remains in effect for low- level mechanical turbulence over and immediately south through west of the mountains of all islands. For now, AIRMET Tango also accounts for sustained surface wind speeds of 30kts in the Alenuihaha Channel and south of the Big Island, but this may be allowed to expire this morning as wind speeds weaken slightly.

Marine

With robust high pressure remaining far north of the area into next week, trade winds will remain breezy to strong over coastal waters.
Also, seas will remain elevated and rough with the persistent strong trades over the next several days. Thus, a Small Craft Advisory (SCA), for winds and seas, has been posted through Sunday afternoon for all coastal waters, and may need to be extended beyond that time frame.
With locally generated wind waves, and strong trade winds upstream from the state, surf along east-facing shores will remain large and turbulent. To account for this, a High Surf Advisory will remain in effect through Sunday night for Kauai, Oahu, Molokai, Maui, and the Big Island. Too, some of this trade wind energy will wrap around into adjacent northern and southern exposures.
As the current northwest swell fades, a reinforcing small to moderate northwest swell will fill in and peak late today into early Sunday. The next following northwest swell will likely be larger than this weekend’s and raise surf to near advisory levels along northern and western exposed shores, beginning late Wednesday into early Thursday. Lastly, south-facing shores will see surf boosted modestly by small swells from the southern hemisphere, along with wrap from the east by the trade wind swell.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Monday for Kauai Windward, Oahu Koolau, Olomana, Molokai Windward, Maui Windward West, Windward Haleakala, South Big Island, Big Island North and East.
Flash Flood Watch through Sunday afternoon for Maui Windward West, Windward Haleakala, Haleakala Summit, South Big Island, Big Island North and East, Big Island Interior.
Winter Weather Advisory until noon HST Monday for Big Island Summits.
Small Craft Advisory until 6 PM HST Sunday for all Hawaiian waters,

Data Courtesy of NOAA.gov