Current Conditions | ||
Temp | ![]() | 1.4 C |
RH | ![]() | 10 % |
Wind | ![]() | NNE 16 mph |
Road | ![]() | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 314 FXHW60 PHFO 160155 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 355 PM HST Sun Dec 15 2019 .SYNOPSIS... Trade winds will strengthen tonight and Monday, with breezy conditions expected into Tuesday. The trades will trend down Wednesday into Thursday, before increasing to locally windy levels late Thursday into next weekend. The trades will continue to deliver low clouds and showers to windward areas with a few showers occasionally spreading leeward. && .DISCUSSION... Trade winds (at times quite strong) will prevail through the upcoming week, supported by a pair of high pressure cells passing far N of the islands, with the central pressure of the second high expected to be anomalously high. Winds may turn SE next weekend as low pressure develops and strengthens W of the islands, with this low potentially impacting island weather in just over a week from now. Moderate trade winds will increase overnight and Monday as high pressure currently NNW of the islands passes to our N, and will remain breezy until a weakness in the ridge passes to the N around Wednesday. An even stronger high is expected to pass N of the islands late Thursday into Saturday, likely bringing a period of locally strong trade winds heading into next weekend. Central pressure of this high is expected to be an unseasonably high 1034 mb as it passes, and model guidance indicates very strong trade winds at the end of the week, with open ocean wind speeds of 30-35 mph near the islands. As low pressure deepens W of the area next weekend, the gradient between the gradually weakening high and the developing low may bring strong SE winds to the state. Confidence is somewhat diminished as to the details, but model guidance has been fairly consistent indicating a somewhat energetic weather pattern in about a week from now as the low nears the islands. In the meantime, expect passing windward showers and moderate trade wind until trade winds increase later tonight and Monday. A weak mid- level shortwave is expected to pass from N to S over the area Monday and Monday night. The combined effects of increased orographic lift supplied by the increased trades, the passing shortwave, and moisture associated with a frontal remnant caught in the trade flow will likely lead to an increase in trade wind showers, and a slightly wetter regime than previously thought. A mid-level ridge will build over the islands Tuesday and Wednesday, supporting a stable island atmosphere, but the trade winds should still be able to muster a few windward showers. With the strong cap in place, the already strong trade winds may become especially gusty Monday night and Tuesday, especially near and downwind of terrain. The mid-level ridge will weaken Thursday and Friday, and increasing low level convergence associated with the new high building N of the area will likely fuel an increase in trade showers, with another frontal remnant potentially introducing moisture into the trade flow as well. && .AVIATION... Strengthening trade winds expected tonight as a high pressure system north of Hawaii settles to the northeast of the area.The trades will focus incoming low clouds and showers over windward slopes resulting in brief mountain obscurations this evening which could increase in coverage late tonight. However, no AIRMETs are in effect at this time. AIRMET Tango will likely be issued later tonight or Monday morning for leeward mountain turbulence due to the strengthening trades statewide. && .MARINE... A 1026 mb high pressure building north of the state tonight will bring an increase in trade winds and will result in strong trades through the first half of the week. Winds may reach gale force Monday night into Tuesday across the Alenuihaha Channel and waters south of the Big Island. Therefore, a Gale Watch is in effect for these waters. Winds may slightly decrease Wednesday night into Thursday, but a new 1035 mb high building north of state will lead to stronger trades towards the end of the week. Gale force winds are likely for the typical windy areas around Maui County and the Big Island Friday into Saturday. Winds will likely remain strong through the next weekend. Forerunners from a new northwest swell will begin to fill in late tonight and the swell is expected to steadily build through the day Monday. Surf will likely reach high end advisory levels Monday night as the swell peaks. Another advisory level northwest swell is expected to steadily build Wednesday night. The combination of strong trade winds and large northwest swells will bring widespread Small Craft Advisory conditions through most of the upcoming week, with Gale warnings possible Monday night through Tuesday and once again Friday into Saturday. With the expected boost in trades throughout the new work week, surf along east facing shores will be on the rise. Surf will likely reach the High Surf Advisory (HSA) criteria of 8 feet for east facing shores later in the week with the stronger surge of trade winds. It should be noted that waters and ocean conditions will be very rough and choppy through most of the week. && .HFO WATCHES/WARNINGS/ADVISORIES... Gale Watch from Monday evening through Tuesday afternoon for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. Small Craft Advisory until 6 PM HST Monday for Alenuihaha Channel- Big Island Leeward Waters-Big Island Southeast Waters. Small Craft Advisory from 6 AM Monday to 7 PM HST Wednesday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters- Kauai Channel-Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel- Maui County Windward Waters-Maui County Leeward Waters-Big Island Windward Waters. Small Craft Advisory until 7 PM HST Wednesday for Maalaea Bay- Pailolo Channel. && $$ DISCUSSION...Birchard AVIATION...Foster MARINE...Kino Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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