textproduct: Eureka

KEY MESSAGES

* Moderate risk for sneaker waves along the Lost Coast and Mendocino Coast through Wednesday.

* Coastal stratus likely to continue to form each night

* Hot temperatures return late week into the weekend.

* Elevated fire danger returns late in the week and at least into next week with increased wind and increasingly hot, dry conditions.

SYNOPSIS

Near to slightly below normal temperatures forecast for the interior areas, while near to above normal coastal temperatures are likely continue through Wednesday. Breezy afternoon winds elevate fire danger in eastern Trinity, eastern Mendocino, and Lake counties. Hot interior temperatures return late this week with a further increasing fire weather risk.

DISCUSSION

The extended period of lighter northerly winds has shut down much of the coastal upwelling. This continues to allow for warmer than average coastal water temperatures, into the low 60s, and a weaker low level inversion. The lack of cool air advection from the coastal waters and quickly dispersing daytime stratus has fed into a positive feedback loop, maintaining warmer temperatures along the coast. The stratus looks to be driven into the North Coast through the afternoon hours Wednesday, likely knocking down temperatures slightly lower than recently observed. Interior temperatures will otherwise will be near or below average Wednesday from an atypical summertime troughing pattern. A pronounced shortwave perturbation will advance over N CA Thursday. Moisture and instability will be very limited, so only mid to high level clouds should result.

A Four Corners/Desert Southwest dome of high pressure will then begin to strengthen Thursday. The 500mb ridge will continue to strengthen, reaching 597 to up to 600dm by Friday. This will translate to hot interior temperatures. Probabilities for interior temperatures over 100 increase going into next week, with high chances (60 to 80%) for temperatures over 100 by Monday, and moderate chances (40%) for temperatures over 104 Tuesday and Wednesday of next week.

Fire weather concerns will become elevated again with the duration of the building heat along will periods of breezy conditions. See the Fire Weather section below. /JJW

AVIATION

06Z TAFs. Stratus reformed Tuesday evening after periods of full clearing and VFR conditions. The marine layer has remained deepened from broad troughing and passing weak shortwaves. A second weak shortwave is forecast to pass through Wednesday. This should maintain mostly MVFR to IFR ceilings. Statistical guidance have higher chances for LIFR ceilings and some fog, but they have not verified well under the atypical summertime troughing regime. Highest chances for LIFR remain north over CEC. Coastal sea surface temperatures have been warmer than average, in the low 60s, and this has contributed to a largely weakened low level inversion. There are growing indications light NW winds will pool up stratus around Humboldt Bay through the afternoon, while clearing occurs elsewhere, though ceiling heights should lift to MVFR levels. VFR conditions will prevail for the interior. Northerly winds will increase through the afternoon hours, with some gusts up 20 kts possible at CEC, ACV and UKI. Stratus will begin expanding back over the coast Wednesday evening, but should not be initially too shallow. /JJW

MARINE

Northerly winds have trended higher over all zones. Winds north of Cape Mendocino look to generally remain below 20 kts through Friday. The focus of stronger northerlies will remain around and south of Cape Mendocino. Northerlies of 20-25 kts in these southern zones, locally with gale conditions up to 30 kts around the cape, can continue to be expected. Short period northerly seas will increase over the waters, along with a small long period southerly swell. A ridge of high pressure will strengthen through the weekend, bringing increased chances for gale strength northerlies over much of the waters. /JJW

FIRE WEATHER

Afternoon westerly breezes will likely bring isolated areas of enhanced fire weather danger and perhaps brief critical conditions locally. Overnight recoveries are expected to be moderate to good, aside from the higher elevations of Lake and eastern Trinity County.

Closer to the coast, a deep marine layer brings high RH and perhaps stratus and/or fog into the river valleys overnight. Afternoon RH ranges from 60s to 80s near the immediate coast to low 20s in interior Humboldt, Del Norte, and western Mendocino Counties Wednesday.

Ridging rebuilds back in starting Thursday, bringing much warmer high temperatures to the interior. Most valleys are forecast to reach the high 90s and triple digits, with highest chances for temperatures over 100 early next week. Afternoon RHs will again be in the teens and 20s for the eastern interior. Troughing to the north will likely enhance winds over the weekend and possibly Monday, increasing the fire weather threat, especially when coinciding with the building heat and low RH. /JJW

BEACH HAZARDS

A long period southerly swell with periods up to 18 seconds remains in from tropical systems in the Eastern Pacific through Wednesday, with easing of size and energy thereafter. This energetic swell will continue to bring a low to moderate risk of sneaker waves that are most hazardous on steep, south and southwest facing beaches along the Lost Coast and Mendocino Coast through Wednesday.

Sneaker waves are a unique hazard, with up to 30 minutes between waves. Large, unexpected waves can sweep across the beach without warning, sweeping people into the sea from rocks, jetties, and beaches. These sneaker waves can also move large objects such as logs, crushing anyone caught underneath. Even ankle to knee deep water can knock you down and drag you out when a sneaker wave hits. Pay attention and stay above the high water line and any wet sand to stay safe. If the ground is wet, waves have surged there recently. Stay safe and never turn your back on the ocean! /JJW

EKA WATCHES/WARNINGS/ADVISORIES

CA... Beach Hazards Statement through Wednesday afternoon for CAZ104-109.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 2 PM PDT Friday for PZZ455-475.