FORECAST DISCUSSION

Synopsis

Light winds can be expected over the next several days with daytime sea breezes and nighttime land breezes dominating. The weather pattern will become a bit more unsettled over the next few days due to a trough of low pressure west of the area. Shower activity is expected to increase later this week and on into the weekend. A frontal boundary is then forecast to reach the islands later this weekend and stall out across the central islands.

Discussion

There are several weather features that will control our islands weather over the next several days. First, a broad upper level trough is centered several hundred miles west and northwest of the state. A surface low along with a developing frontal boundary are associated with this upper trough. There is also a weak surface trough centered near The Big Island. The sets the islands up for a rather unsettled weather pattern for the next several days. Radar imagery is currently showing just a few showers over and around the Aloha State this morning. However satellite imagery shows increasing high cloudiness moving in from the southwest. Presently most of these clouds are thin, but they are expected to gradually thicken up later today and on into Thursday. Winds will remain light over the next few days favoring daytime sea breezes and nighttime land breezes. Some clouds are expected to build up over interior areas today with some showers a distinct possibility. With weak forcing in place most showers are not expected to be to heavy. Over the next few days, a series of shortwave trough will pass across the area. This combined with abundant low level moisture should allow for an increase in shower activity. The moisture may be deep enough to allow for some wintery weather over The Big Island summits, thus a Winter Weather Advisory is posted beginning this evening. As these shortwaves pass across the area, shower chances will likely increase but timing and location remains problematic as low level forcing remains weak. Thus unsettled weather can be expected at times through Saturday but rainfall will not occur all the time and over all locations. By Sunday models indicate the upper trough will be moving eastward with a surface frontal boundary moving over the state. An increase in showers will likely accompany the front. Light northeast winds are forecast to fill in behind the front. However models indicate that the frontal boundary will likely stall in the island vicinity. Thus wherever the front stalls along with the northeast low level wind flow, showers will likely continue to fall but become more windward and mauka oriented.

Aviation

Regional radars show the strongest shower activity over the coastal waters overnight due to offshore land breezes, though enough of a background flow has kept some clouds across eastern sections of the islands. Conditions are primarily VFR, except for occasional MVFR ceilings in showers. Developing onshore winds today will lead to interior clouds and showers by afternoon, with localized MVFR conditions as well. A band of moisture east of the Big Island will lead to more widespread MVFR conditions across windward and southeast sections.

Marine

Mainly gentle winds will prevail through at least the weekend. A weak surface ridge located 150 to 200 nm north of Kauai will shift over the islands on Thursday, causing the weak easterly winds to veer out of the southeast and south. Northerly winds are expected to develop over the western portion of the island chain on Sunday and Monday. A northwest swell will peak this afternoon and evening, producing surf below advisory levels on north and west facing shores. After this swell declines on Thursday, very small surf will prevail on all shores into early next week.

HFO Watches/Warnings/Advisories

Winter Weather Advisory from 6 PM this evening to 6 AM HST Friday for Big Island Summits.

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Synopsis/Discussion...Burke Aviation...Bravender Marine...Wroe

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