Light to moderate trade winds will produce light rainfall over mainly windward areas into the evening. Low pressure will develop north of the state on Wednesday, causing winds to weaken and shift out of the south and allowing sea breezes to produce a few interior showers in the afternoon. Deep southerly winds will draw tropical moisture over the portions of the island chain Wednesday night through at least Thursday, bringing some potential for flooding rainfall. The low will weaken several hundred miles northwest of Kauai Friday and Saturday then lift away on Sunday, though a few heavy showers may linger through the weekend under light winds. Light trade winds are expected to return early next week.
Stable trade winds will continue to slowly weaken today as a cold front nearly 1000 miles north of Kauai pushes a surface high eastward. A weakening low to mid level ridge over the islands will maintain stable conditions, with small pockets of moisture producing modest rainfall over windward areas. Aside from the typical afternoon scattered showers over the Kona slopes, leeward sections will be mostly dry.
Winds will weaken considerably tonight and begin to shift out of the east to east-southeast as surface low pressure develops along the stalling front roughly 800 to 900 miles north of Kauai. No significant rainfall is expected, and land breezes could push most showers offshore in the predawn hours.
The low will intensify and drift to about 700 miles north of Kauai on Wednesday. Since this feature will be somewhat far away from the islands, local winds will shift out of the southeast to south but are only expected to be at gentle to moderate strength. As a result, expect afternoon sea breezes to overpower the background flow along north shores and generate isolated interior showers in the afternoon. Stability will decreasing, though heavy showers are not expected at this time.
A humid southerly flow will bring increased chances for widespread rainfall Wednesday night through at least Thursday. The low be at its strongest and closest to the islands at this time, possibly within 600 miles north of Kauai. Moderate southerly flow will draw up an area of deep tropical moisture over the islands while a jet stream entrance region along the eastern flank of the low provides some moist ascent. This could lead to a period of moderate to locally heavy rainfall favoring the western half of the island chain but possibly extending eastward to all islands. Due to the southerly flow, leeward areas will be exposed to potentially heavy rainfall, and while we have held off on issuing a Flood Watch, we will be taking a closer look today. While gusty downsloping winds are typically a concern in this setup, the flow does not appear to be strong enough for winds to reach advisory levels.
The low will stall and begin to gradually weaken roughly 700 miles northwest of Kauai on Friday. The jet stream on its eastern flank will retreat north of the islands. This will reduce upper level support for widespread heavy rainfall. However, light southerly winds will persist, with daytime sea breezes supporting spotty afternoon showers and dew points creeping into the mid 70s.
The humid flow will gradually shift out of the southeast on Saturday. The GFS and ECMWF suggest that the highest rainfall chances will be along a weak surface convergence zone near Oahu and Kauai, and ridging aloft will build in from the east and provide increased stability for at least Big Island. The low is expected to fill as it lifts off to the northeast Sunday. Aside from the possibility of variable winds on Kauai, conditions should be similar to Saturday.
Light trade winds are favored to return Monday.
Background trade winds will be weaker today, then continue to weaken and veer more southerly tonight into Wednesday due to a nearby surface trough. This will cause a hybrid light trade wind and sea breeze pattern. Terrain sheltered areas will be more likely to see afternoon cloud and shower development as a result. Meanwhile, brief and isolated shower activity is expected over windward and mountain areas. MVFR conditions will occur within showers, while VFR prevails elsewhere.
There are currently no AIRMETs in effect, though mountain obscuration could become an issue for portions of the state later today.
Winds will weaken today as a low pressure system and an associated cold front develops north of the state and approaches from the northwest. A trough extending from this low is forecast to move into the northwest offshore waters by Thursday. The low will stall north of the islands and draw moisture out of the tropics and over the area through the second half of the week, so expect an increase in showers with moderate south to southeast winds. The trough could potentially linger into the weekend.
Offshore buoy observations show a southerly swell around 3.5 ft with 16 second period, which will push surf for south-facing shores close to advisory level by this afternoon and last through tonight. By Wednesday, this swell will begin to fade. Surf is then likely to be held near seasonal averages for the remainder of the week, maintained by a mix of new, small south swells.
A long-period northwest swell will arrive today, pushing surf for north-facing shores up tonight to near moderate levels on Wednesday. Small to moderate surf is then forecast through the rest of the week even as swell energy becomes shorter period, since it will be reinforced by a low to the north-northwest of the Hawaiian Islands. Surf along east facing shores will remain small as local winds remain fairly weak.
A small, long-period west swell originating from Typhoon Choi-wan is forecast to reach the islands Thursday into the weekend, which may produce moderate surf for west-facing shores.
None.
