Hilo

Today: Showers likely, with thunderstorms also possible after 1pm. Mostly cloudy, with a high near 76. Northwest wind 5 to 9 mph becoming east in the afternoon. Chance of precipitation is 60%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Showers likely and possibly a thunderstorm. Mostly cloudy, with a low around 63. East wind 5 to 9 mph becoming west after midnight. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tuesday: Scattered showers, with thunderstorms also possible after 1pm. Partly sunny, with a high near 77. West wind around 6 mph becoming east in the afternoon. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Kona

Today: Scattered showers and thunderstorms after noon. Mostly sunny, with a high near 79. Northwest wind 5 to 9 mph becoming south in the afternoon. Chance of precipitation is 40%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Isolated showers before midnight. Partly cloudy, with a low around 61. Calm wind. Chance of precipitation is 20%.

Tuesday: Scattered showers and thunderstorms after noon. Mostly sunny, with a high near 79. West wind 5 to 8 mph. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Waimea

Today: Scattered showers, with thunderstorms also possible after noon. Mostly cloudy, with a high near 74. Breezy, with a northeast wind 10 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 52. Northeast wind 5 to 7 mph becoming west after midnight. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Tuesday: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 74. West wind 3 to 5 mph. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Kohala

Today: Showers likely, with thunderstorms also possible after noon. Mostly cloudy, with a high near 70. Breezy, with an east wind 17 to 22 mph, with gusts as high as 31 mph. Chance of precipitation is 70%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers. Mostly cloudy, with a low around 45. East southeast wind 7 to 9 mph becoming southwest after midnight. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tuesday: Scattered showers, then showers likely and possibly a thunderstorm after noon. Partly sunny, with a high near 70. West southwest wind around 6 mph. Chance of precipitation is 60%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

South Big Island

Today: Scattered showers and thunderstorms after noon. Mostly sunny, with a high near 79. Breezy, with an east wind 18 to 22 mph, with gusts as high as 28 mph. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers. Mostly cloudy, with a low around 69. Breezy, with an east northeast wind 15 to 17 mph, with gusts as high as 22 mph. Chance of precipitation is 30%.

Tuesday: A 20 percent chance of showers and thunderstorms after noon. Mostly sunny, with a high near 79. Breezy, with an east wind 13 to 15 mph, with gusts as high as 18 mph.

Puna

Today: Showers likely, with thunderstorms also possible after noon. Mostly cloudy, with a high near 75. West wind 7 to 13 mph becoming east northeast in the morning. Chance of precipitation is 70%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Showers likely, mainly before midnight. Mostly cloudy, with a low around 61. East southeast wind 5 to 9 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Tuesday: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 76. South southeast wind 8 to 11 mph. Chance of precipitation is 30%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Waikoloa

Today: A 20 percent chance of showers and thunderstorms after 1pm. Mostly sunny, with a high near 80. East wind 5 to 10 mph becoming light and variable in the afternoon.

Tonight: A slight chance of showers and thunderstorms before 7pm, then isolated showers between 7pm and 1am. Partly cloudy, with a low around 61. Light and variable wind becoming southeast around 6 mph after midnight. Chance of precipitation is 20%.

Tuesday: Scattered showers and thunderstorms after 1pm. Mostly sunny, with a high near 80. Light and variable wind becoming west northwest 5 to 7 mph in the afternoon. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Detailed Forecast

Synopsis

The trade winds will gradually weaken through this evening. Somewhat drier conditions will occur over the smaller islands, with brief showers mainly along windward facing sections through this afternoon. Widespread showers and a chance of afternoon thunderstorms are expected over the Big Island. As a front approaches the islands from the northwest, a land and sea breeze pattern will likely set up from tonight through Tuesday. Wet weather is forecast to develop across most of the state from Wednesday through Thursday as the frontal boundary moves across the western islands.

Discussion

A 1037 mb surface high is centered near 37N 140W, or more than 1450 miles northeast of Hilo. A surface ridge extends west- southwest from this feature through a point less than 500 miles north of Lihue. The relatively tight pressure gradient south and southwest of these features is maintaining breezy trade winds across the state early this morning. Elsewhere, the leading edge of a band of clouds and showers associated with a cold front is evident about 750 miles northwest of Kauai. This leading edge is moving toward the east-southeast at about 25 mph. As a result, it is gradually weakening the pressure gradient across the state.
Aloft, an upper-level trough continues to linger just to the east and northeast of the Big Island. This will maintain atmospheric instability over the Big Island today. This instability combined with increased moisture is expected to result in clouds, showers, and a slight chance of afternoon thunderstorms developing over portions of the Big Island. Elsewhere, expect some low clouds over east and southeast facing sections of the state into this evening. A few showers are also possible over some leeward sections of the smaller islands.
Significant changes to our weather pattern can be expected from tonight through Tuesday as the front moves closer to the state. The background flow will continue to weaken, and shift from the south-southeast over the eastern islands, and from the south- southwest over the western islands. This flow will transport increasing moisture into the state. The winds will also likely be weak enough to allow an alternating local nighttime land breeze and afternoon sea breeze pattern to set up during this time period. Therefore, clouds and showers may develop over the interior sections of the islands Tuesday afternoon. The increasing moisture also may result in a chance of thunderstorms over portions of the Big Island again Tuesday afternoon.
By Wednesday, the forecast models depict a weakening frontal system near Kauai, since an upper-level trough associated with the front will likely remain north of the area. The models also seem to agree that additional moisture will be transported over Oahu and Maui County in the southerly flow to the east of this feature. Therefore, expect an increase in cloud cover and showers, especially in convergence bands that develop over the western and central islands. Note that there is some potential for winter weather developing around mid-week over the Big Island Summits if the deeper moisture makes it far enough east. The weakening frontal boundary appears to move across Kauai and Oahu, and may reach Maui County before it stalls and weakens. It may transition to a surface trough Thursday or early Friday before it shifts westward due to surface high pressure building northeast of the state. This high pressure may allow trade winds to return to the islands by next weekend.

Aviation

Moderate trade winds will gradually ease today, and become light and variable tonight as a cold front approaches from the northwest. Showers will favor windward and mauka areas through the day, with rather dry conditions persisting over the smaller islands. As the trades weaken late this afternoon, a few showers may develop over interior and leeward sections of the islands which should fizzle out this evening as land breezes develop and shift most of the shower activity offshore. Brief MVFR conditions will be possible here, although predominantly VFR conditions should prevail. Over windward Big Island a rather wet day can be expected however, with MVFR cigs/vsbys common, including PHTO. Conditions should improve over the Big Island this evening as well. Additionally, a thunderstorm or two can’t be ruled out over the Big Island interior this afternoon.
AIRMET Sierra remains in effect for mountain obscuration over windward sections of the Big Island and will likely continue through much of the day.
AIRMET Tango remains in effect for moderate low-level turbulence over downwind of the terrain of all islands. This AIRMET will likely be cancelled later today.

Marine

A cold front approaching the waters from the northwest will significantly weaken recent fresh to strong trade winds. Seas will fall below Small Craft Advisory (SCA) levels across most Hawaiian coastal waters this morning. Winds and seas within the Alenuihaha Channel will be close to SCA criteria early today and will warrant a continuation of an SCA for the channel. Weakened trades will veer more southerly Tuesday. The front is forecast to reach the northwest coastal waters by Wednesday and then stall out over more central waters late in the week.
The far northeast high is still generating a strong trade fetch upstream of the islands. Thus, while the short period east trade wind swell is peaking today it will slowly subside through the week. East-facing shoreline surf will begin to lower through the day in direct response to weakening trades that will transition to light southerlies over the area with the approach of a cold front northwest of the state. The High Surf Advisory (HSA) for the eastern shores of Kauai, Oahu, Molokai, Maui and Big Island is in effect until 6 PM HST this evening due to the delayed lowering of surf along these eastern exposures. The small north northeast swell that filled in this past weekend will diminish tonight through Tuesday. A couple of small, short period northwest swells will move around the islands through Tuesday. A small, compact low approximately 500 nm south of the Aleutian Islands this morning will send the next appreciable northwest swell our way. This northwest swell is scheduled to arrive in the northwest waters during the day Tuesday and then build down the chain through Thursday. During the peak of the swell surf heights along north and west-facing shores of the smaller islands may reach low end HSA thresholds Wednesday night through Thursday. This northwest swell will gradually decline Friday and Saturday. A series of storms south of New Zealand have been sending pulses of long period swell energy toward the local waters. These very small, long period south swells could arrive as early as Tuesday night and provide a small boost to mid to late week south shore surf.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Kauai Windward, Oahu Koolau, Olomana, Molokai Windward, Maui Windward West, Windward Haleakala, Big Island North and East.
Small Craft Advisory until 6 PM HST this evening for Alenuihaha Channel.

Data Courtesy of NOAA.gov