FORECAST DISCUSSION

Update

Afternoon cloud cover was nudged upward across leeward terrain. Otherwise, the forecast is on track.

Synopsis

Trade winds will strengthen today and Monday, and will be locally breezy for The upcoming week. While a drier than normal trade wind weather pattern is expected today and tonight, a short-lived increase in trade showers is expected early Monday. Beyond that, a typical trade wind weather pattern is expected this week, with clouds and brief showers favoring windward slopes and coasts, mainly during nights and mornings. While leeward areas will be mostly dry, leeward Big Island will see afternoon and evening clouds, and a few showers.

Prev discussion

/ISSUED AT 400 AM HST/ A stable trade wind pattern is over the islands this morning, with just a few showery low clouds approaching the islands from the E. High pressure currently building to the distant NW of the islands is supporting increasing trade winds, and will be the primary surface feature driving island weather this week as it tracks steadily eastward. While a drier-than-normal trade wind weather pattern is expected today and tonight, a short-lived increase in trade wind showers is anticipated early Monday. This is expected as an area of low-level moisture associated with a weak mid-level trough, still about 500 miles E of the islands, arrives on the trade wind flow. While this will bring an increase in mainly windward showers, significant rainfall accumulations are not expected. The high passing well N of the area will support locally breezy trade winds, and a typical trade wind weather pattern will prevail from later Monday through at least Friday, with clouds and showers over windward areas most active during nights and mornings. Heading into next weekend, the GFS and ECMWF are somewhat consistent in depicting an increase in moisture arriving from the E and SE, despite some differences in their depiction of synoptic features. Using a blend of these solutions, the long-term forecast grids were modified to increase PoPs next weekend.

Aviation

Trade winds in the light to moderate range will strengthen today as a strong surface high far northwest will move to far north of the state in the next few days. Expect windward sections of the islands to see some MVFR ceilings at times as the trades bring low clouds with embedded showers to the area. Lee areas of the Big Island may also see brief MVFR ceilings this afternoon. Otherwise, VFR conditions will prevail for most areas. Increasing trade winds may lead to the issuance of AIRMET TANGO for turbulence later today.

Marine

A high pressure cell building to the distant NW of the islands is bringing an increase in trade wind speeds, and an overnight ASCAT pass indicated winds up to 25 kt in the Alenuihaha channel. With winds expected to increase further, a Small Craft Advisory (SCA) has been issued for the typically windy marine zones around the Big Island and Maui. The SCA is posted through Tuesday night, although it is expected that it will need to remain in place through much of the week. Surf will be small, especially by Hawaii standards, through the next week. A series of mainly small pulses of SSW swell will continue to bring small surf to S facing shores. A very small, relatively short- period NW swell is already diminishing and this swell will fade today. A new relatively short-period NNW swell is expected Monday and Tuesday, but resulting surf along N and W facing shores will be small. Increasing trade winds will lead to gradually increasing wind waves that will drive moderate short-period surf along E facing shores.

HFO Watches/Warnings/Advisories

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

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Update...Wroe Prev Discussion and Marine...Birchard Aviation...Hui

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