Photo Credit: James Grenz

Hilo

Today: Scattered showers. Mostly cloudy, with a high near 77. Southwest wind 5 to 8 mph becoming east in the morning. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely, mainly before midnight. Cloudy, with a low around 63. South wind around 6 mph becoming light and variable. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Monday: Showers likely, mainly before noon. Partly sunny, with a high near 78. East southeast wind 5 to 8 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Kona

Today: Scattered showers after noon. Partly sunny, with a high near 79. Calm wind becoming west northwest 5 to 9 mph in the morning. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Mostly cloudy, with a low around 63. Calm wind becoming north 5 to 8 mph after midnight.

Monday: Scattered showers after noon. Mostly sunny, with a high near 81. Light and variable wind. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Waimea

Today: Scattered showers, mainly before 1pm. Partly sunny, with a high near 76. Breezy, with a northeast wind 10 to 17 mph, with gusts as high as 24 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers, mainly after 7pm. Mostly cloudy, with a low around 50. North northeast wind 5 to 14 mph, with gusts as high as 18 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Monday: Scattered showers. Partly sunny, with a high near 76. East wind 5 to 9 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Kohala

Today: Scattered showers. Mostly cloudy, with a high near 73. Windy, with a northeast wind 19 to 29 mph decreasing to 5 to 15 mph in the afternoon. Winds could gust as high as 41 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely. Cloudy, with a low around 44. East northeast wind 5 to 9 mph becoming west after midnight. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

Monday: Showers likely, mainly before noon. Partly sunny, with a high near 72. East wind 11 to 13 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Isolated showers after noon. Widespread haze. Mostly sunny, with a high near 81. Windy, with an east wind 24 to 29 mph, with gusts as high as 37 mph. Chance of precipitation is 20%.

Tonight: Isolated showers. Widespread haze. Mostly 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: Scattered showers, mainly after noon. Widespread haze. Mostly sunny, with a high near 81. Breezy, with an east wind around 21 mph, with gusts as high as 26 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Puna

Today: Scattered showers. Mostly cloudy, with a high near 76. West northwest wind 7 to 13 mph becoming east in the morning. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Showers likely, mainly after midnight. Cloudy, with a low around 61. East wind 5 to 8 mph becoming southwest after midnight. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Monday: Scattered showers. Partly sunny, with a high near 77. East northeast wind 7 to 10 mph. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.

Waikoloa

Today: Mostly sunny, with a high near 80. East northeast wind 6 to 13 mph becoming northwest in the afternoon.

Tonight: Partly cloudy, with a low around 61. East northeast wind 6 to 11 mph becoming light east after midnight.

Monday: Sunny, with a high near 82. Light and variable wind.

Detailed Forecast

Synopsis

Breezy trade winds will transport brief trade showers mainly over windward facing sections of the state today. A surface low pressure system developing far northwest of Kauai will likely cause the winds to become lighter across the area starting Monday. The weaker winds are expected to allow daytime sea breezes to develop, which may produce clouds and showers over interior and mauka sections during the afternoon hours on Monday and Tuesday. A new surface high building far north of the area around mid-week will likely produce a wet trade wind pattern starting Wednesday, and continuing through next weekend.

Discussion

A 1042 mb surface high pressure system, which is centered far north of the islands near 47N 158W, is gradually building as it moves slowly eastward. As a result of the tight pressure gradient across the islands, expect breezy trade winds to persist into tonight. Aloft, there is a weak upper-level ridge near the eastern islands, while an upper-level low is located about 950 miles west-northwest of Kauai. Satellite imagery and radar reflectivity data show patches of low clouds with embedded showers being transported by the trades into the islands. Most of these showers are expected to fall along windward facing sections through this evening. The breezy trade winds may also carry some showers over to leeward sections of the smaller islands, especially this morning. In addition to the low clouds, cirrus clouds continue to stream up from the southwest across the state. These high clouds, which consist of ice crystals, are being carried around the periphery of the circulation associated with the upper-level low.
The forecast guidance continues to show a surface low pressure system developing far northwest of Kauai on Monday. This will likely weaken the pressure gradient across the state, and cause the background low-level flow to weaken. This weaker wind pattern will likely allow alternating local afternoon sea breezes and nighttime land breezes to become established over most of the individual islands Monday and Tuesday. The ample daytime heating combined with sea breeze convergence and modest low-level moisture will likely allow clouds and showers to form over interior and mauka sections during the afternoon hours. There may be enough instability across the area to allow for some locally heavy showers, especially over the leeward slopes on the Big Island Monday and Tuesday afternoons.
By Wednesday, the surface low will move away at the same time a new area of high pressure begins to build far north of the islands. This should cause the trade winds to strengthen again starting around mid-week. These breezy trade winds will likely persist from Wednesday through next weekend. A mid-level trough setting up just northeast of the islands during the second half of the week may also cause some destabilization of the atmosphere. The forecast models depict bands of clouds and showers being transported into the islands by the low-level trade wind flow. The slightly unstable atmospheric conditions may enhance some of these low clouds and showers, so expect a wet trade wind pattern during the second half of this week, especially over windward facing sections. The gusty trades may also carry a few showers across to leeward sections of the smaller islands.

Aviation

Strong high pressure far north of the state will continue to support moderate to locally strong trade wind flow. The atmosphere is increasingly stable and incoming low-level moisture is limited. Therefore VFR conditions will prevail. Passing showers will bring brief periods of MVFR VIS/CIG, mainly to windward slopes and coasts.
Light afternoon sea breezes will encourage further shower development along the Leeward slopes of the Big Island. Shower , however, will be limited due to a strengthening inversion around 10 kft which will inhibit vertical development.
AIRMET TANGO remains in effect for both upper and lower level turbulence. Low-level mechanical turbulence to the lee of higher terrain is expected due to the increased trade winds. Moderate turbulence aloft is the result of a trough aloft to the west of the islands, which is also the source of the high clouds streaming across the state.

Marine

High pressure north of the state will keep fresh to strong trades in place through tonight. A storm system developing northwest of the islands will ease the trades into the light to moderate range Monday and Tuesday. The trades will strengthen Tuesday night and reach fresh to strong levels Wednesday into next weekend as a new strong high builds north of the island chain. A Small Craft Advisory remains in effect through 6 PM this evening from the leeward Oahu waters eastward, and through 6 AM Monday for most waters around Maui and the Big Island. The SCA may need to be extended in time for portions of the marine area later today.
A new northwest swell will build this morning, then peak this afternoon into this evening, giving north shore surf a little bump. The swell will be on the decline later tonight and Monday with a very small day in store for Tuesday. Overlapping north and west-northwest swells are expected to give a small boost to surf along north and west facing shores again Wednesday and Thursday. Surf will then return to very small levels Friday, with nearly flat conditions expected next weekend.
Surf along east facing shores will hold steady through tonight, then drop a notch Monday through Wednesday as the trades ease slightly over and upstream of the islands. East shore surf should then trend upward Thursday and rise above normal levels Friday through next weekend.
South shore surf will continue to run above seasonal levels through the next 7 days, as overlapping south swells continue to move through the islands. The largest of these swells is expected Monday through Wednesday, although surf heights will hold below advisory thresholds.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST this evening for Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters.

Data Courtesy of NOAA.gov