Hilo

Today: Occasional showers. High near 76. East wind around 10 mph. Chance of precipitation is 80%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Occasional showers. Low around 64. Light west southwest wind. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.

Monday: Showers likely, mainly before noon. Mostly cloudy, with a high near 78. East wind around 11 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Kona

Today: Scattered showers and thunderstorms after 1pm. Increasing clouds, with a high near 79. West wind around 7 mph. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers and thunderstorms before 1am, then isolated showers. Cloudy, then gradually becoming partly cloudy, with a low around 62. West wind around 8 mph becoming east southeast in the evening. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Monday: Isolated showers before 7am, then scattered showers after 1pm. Increasing clouds, with a high near 79. East southeast wind around 9 mph becoming west in the morning. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Waimea

Today: Showers likely, mainly before noon. Partly sunny, with a high near 74. East northeast wind around 14 mph, with gusts as high as 18 mph. Chance of precipitation is 60%. New precipitation amounts between a quarter and half of an inch possible.

Tonight: Showers likely. Mostly cloudy, with a low around 53. Breezy, with an east wind around 15 mph, with gusts as high as 21 mph. Chance of precipitation is 60%. New precipitation amounts between a quarter and half of an inch possible.

Monday: Scattered showers. Partly sunny, with a high near 75. Breezy, with an east northeast wind around 17 mph, with gusts as high as 24 mph. Chance of precipitation is 50%. New precipitation amounts between a quarter and half of an inch possible.

Kohala

Today: Showers likely. Cloudy, with a high near 70. Northeast wind around 13 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Showers likely. Mostly cloudy, with a low around 46. Breezy, with an east wind around 15 mph, with gusts as high as 21 mph. Chance of precipitation is 70%. New precipitation amounts between a quarter and half of an inch possible.

Monday: Occasional showers. High near 71. Breezy, with a northeast wind around 15 mph, with gusts as high as 21 mph. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.

South Big Island

Today: Sunny, with a high near 76. Windy, with an east northeast wind around 24 mph, with gusts as high as 31 mph.

Tonight: Isolated showers. Partly cloudy, with a low around 71. Windy, with an east northeast wind around 25 mph, with gusts as high as 32 mph. Chance of precipitation is 20%.

Monday: Sunny, with a high near 76. Windy, with an east northeast wind around 26 mph, with gusts as high as 34 mph.

Puna

Today: Occasional showers. High near 75. East northeast wind around 9 mph. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.

Tonight: Occasional showers. Low around 62. Light west northwest wind. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.

Monday: Showers likely. Mostly cloudy, with a high near 75. East northeast wind around 13 mph. Chance of precipitation is 70%. New precipitation amounts between a quarter and half of an inch possible.

Waikoloa

Today: A 20 percent chance of showers and thunderstorms after noon. Mostly sunny, with a high near 80. Northwest wind around 7 mph.

Tonight: A slight chance of showers and thunderstorms. Partly cloudy, with a low around 62. East northeast wind around 8 mph. Chance of precipitation is 20%.

Monday: Mostly sunny, with a high near 81. North northwest wind around 9 mph.

Detailed Forecast

Synopsis

High pressure building far north of the state will gradually strengthen the trade winds. An upper level trough moving over the islands will bring some high clouds and enhance the trade wind showers today, particularly for Maui and the Big Island. Trade winds will decrease on Wednesday and remain at moderate strength into next weekend, leading to more typical trade wind weather.

Discussion

Some modification to the grids with the morning package, but the overall forecast philosophy remains the same. Have lowered the PoPs for some areas on Kauai and Oahu today, in line with some of the higher resolution model guidance. Have boosted QPF values for windward areas, particularly Maui and the Big Island, in light of rainfall totals overnight, and what a blend of the models shows through tomorrow night. Have also tapped down wind speeds just a bit during the middle to end of the week in line with a trend in the models which show winds won’t be quite as strong as previously forecast, but still expecting moderate trades to end the week.
High pressure to the north will maintain the trade wind flow. The nearly stationary surface low to the northeast will remain in place for the next few days. As the high slowly moves to the east and strengthens, the resultant pressure gradient over the islands is expected to tighten which will cause a bit of an uptick in our winds. Frontal remnants riding in on the trades have been reaching the windward sides of the islands with the main focus overnight being over Maui, with some making it to Oahu.
An upper level trough axis located roughly northeast to southwest over the western end of the state overnight will continue to have impacts on our weather into tonight. High clouds are streaming over the islands from the southwest and west on the east side of the trough. The trough is also bringing colder upper level temperatures to the islands. Both Lihue and Hilo overnight soundings had 500 mb temperatures near -12 C (below normal). Precipitable water (PW) at Lihue was around 1 inch (near normal for April), while at Hilo it was 1.43 inches (a little above normal). The trough is expected to be east of the islands by tomorrow morning. There is the chance for a thunderstorm or two to pop on the Big Island this afternoon/evening, and as mentioned above, rainfall totals for windward areas in particular are likely to be higher than normal trade winds. Along with all of this, there is the possibility that any precipitation that reaches the Big Island summits will fall in the form of freezing rain and/or snow.
Lower PW values are expected to spread across the islands from the north behind this upper level trough, and 500 mb temperatures are expected to return to near normal, both of which will help to usher in a drier and more stable airmass. This should result in a downward trend in shower activity for the start of the new work week. Expect breezy trades to linger into at least Tuesday as high pressure holds to the north. Showers should once again become focused along windward slopes with mainly dry conditions leeward, aside from typical afternoon showers on the Kona slopes.
Trade winds will likely drop a notch on Wednesday and remain at moderate strength into next weekend. The GFS and ECMWF show a slow moving mid to upper level trough just east of the state and a ridge to the west. The islands should remain just far enough away from the trough to produce a stable trade wind flow and typical trade wind weather. However, there is some uncertainty at this time.

Aviation

Strengthening trades have prompted issuance of AIRMET Tango for lee turbulence for Big Island through Maui. There is potential for additional expansion during the forecast period especially as the trade inversion strengthens from north to south. In the near term, MVFR still prevails over Windward Big Island and Maui where AIRMET Sierra remain in effect. As trades usher in a greater coverage of low clouds and showers this afternoon into this evening, MVFR will become increasingly likely for Molokai through Kauai.
AIRMET Sierra for mountain obscuration is in effect for Windward Big Island and Maui.
AIRMET Tango for lee turbulence is in effect for Big Island and Maui.

Marine

High pressure north of the state will keep fresh to strong trade winds in place through Wednesday. The trades will ease into the moderate to fresh range late in the week as the high north of the islands weakens. A Small Craft Advisory (SCA) is now in effect for the typically windy waters around Maui and the Big Island through 6 PM Tuesday. The SCA will likely need to be expanded to include most – if not all – marine zones tonight through Tuesday as the trades peak.
The current north swell will build during the next couple days and gradually shift around to a more northeast direction. Surf along north and east facing shores will follow suit with a steady rise, with surf likely reaching High Surf Advisory (HSA) thresholds along east facing shores by late Monday, then holding at advisory levels through Thursday. This swell will then slowly lower Friday through next weekend. A series of small south swells will move through the islands during the next 7 days, keeping south shore surf near the seasonal average for early spring.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov