Fairly dry conditions continue into the first half of next week as trade winds steadily strengthen into the breezy to strong range by Wednesday and Thursday. Wind speeds will then start a gradual decline into the moderate to locally breezy range from Thursday night into next weekend. An upper level low passing just south of the islands by late Friday may enhance rainfall coverage over the eastern half of the state lasting into next weekend.
The satellite and local radar imagery around the Hawaiian Islands this evening continues to show fairly stable clouds with just a few showers popping up over the coastal waters this evening. Upper air radiosonde balloon observations from Lihue and Hilo earlier this afternoon at 2 PM HST (00Z) show subsidence temperature inversion heights in the 5,500 to 6,500 foot range. These low inversion heights are caused by the downward vertical motions (subsidence)under the upper level ridge, which warms and dries the atmosphere aloft, creating a stable temperature inversion layer, limiting vertical cloud growth, and decreasing rain shower activity. These more stable conditions will continue into the first half of this week.
The main weather story for the next several days will be a steady strengthening of the trade winds from moderate to breezy levels by Monday, then increasing into the breezy to windy range by Tuesday, with wind speeds peaking on Wednesday across the island chain. Wind speeds will likely reach wind advisory thresholds for some of our windier zones possibly starting on Tuesday night. The highest summits of Mauna Kea and Mauna Loa where wind speeds are expected to jump up to warning levels as early as tomorrow morning as an upper level jet streak dives down over the area. As such, a High Wind Warning has been issued for these summits starting Monday morning at 6 AM HST.
Relative humidity levels do not appear to fall low enough in the windier leeward areas to reach fire weather concerns at this time. We will continue to closely monitor these wind and humidity levels as this weather pattern evolves through the week.
In the long range outlook, global weather models continue to show an upper level cut off low moving into the Hawaii region. Current operational runs show the center of this low passing south of the Big Island by Wednesday. This low may bring up tropical moisture and instability into the windward and southeastern slopes of the Big Island, enhancing shower activity from Friday into next weekend. The American (GFS) model also shows windward Maui picking up additional shower activity by Saturday. Rainfall impacts for the eastern islands will to a large degree depend upon the strength and final track of this upper level low. Stay tuned for more details as the forecast time period grows shorter.
Light to moderate trades strengthen through mid- week. Low cigs and SHRA should mainly impact windward and mauka locations. Brief MVFR conds can be expected in SHRA otherwise VFR conds should prevail.
AIRMET Tango is in effect for mod turb btn FL180 and FL350 for the entire chain. With trades on the rise, AIRMET Tango may also be needed for mod low level turb over and downwind of terrain tomorrow.
Easterly trade winds will steadily strengthen through the first half of the week, reaching moderate to strong levels on Monday. By Tuesday, fresh to strong breezes are expected across most waters as a surface ridge builds to the north. Small Craft Advisory (SCA) conditions are likely for the windier waters near Maui County and the Big Island beginning early Monday, with an expansion to additional waters by Tuesday due to stronger winds and building seas. These conditions are expected to persist through the rest of the week.
Surf along north and west-facing shores will continue easing this evening but is expected to trend upward on Monday as a fresh north-northwest swell builds down the island chain. Evening observations at northwest buoys upstream of Kauai indicate very small energy within the 19-21+ second bands, likely signaling the arrival of this new swell. Heights could approach low-end advisory levels late Monday through Tuesday if these swells come in larger than predicted. A slight downward trend is expected during the second half of the week, with surf holding steady near or slightly below seasonal averages into the weekend.
Surf along south-facing shores will remain up through Monday, driven by an out-of-season south swell, which will gradually subside by Tuesday. Seasonal conditions will return midweek, with a mix of smaller southeast and south-southwest swells.
East-facing shores will experience increasing surf through the week as trade winds strengthen locally and expand upstream across the eastern Pacific.
High Wind Warning from 6 AM to 6 PM HST Monday for Big Island Summits.
Small Craft Advisory from midnight tonight to 6 PM HST Wednesday for Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.
