Half Moon Bay is the Bay Area's most reliably cool and foggy coastal town. While the rest of the region swings between summer heat and winter storms, Half Moon Bay stays remarkably steady. It is foggy in summer, mild and often sunny in fall, rainy in winter and cool and green in spring. The town faces the open Pacific along San Mateo County's western shore. That ocean shapes its character and is why most Bay Area residents bring a jacket no matter what their weather app says.
For water conditions, check recent NOAA offshore water temperatures. The Half Moon Bay offshore buoy is a regional reference rather than a reading at the harbor or the surf line.
Summer Fog: The Baseline Condition
In Half Moon Bay, summer fog is less a weather event than the normal state of things. The marine layer fills the coast each morning, and on many summer days it never fully clears. July and August highs average around 65°F, and the ocean offshore sits in the low to mid 50s, some of the coldest water on the central California coast. Pacifica, farther up the coast, is often cooler still, with summer afternoons in the low 60s, because its valleys open straight to the ocean.
The usual summer wind blows from the northwest, straight off the cold ocean, and it keeps temperatures from climbing even when the fog breaks. On most summer mornings the town is fogged in and the harbor is barely visible through the gray. The wind makes it feel colder than the thermometer says. Locals and the harbor's fishing crews treat fleece and layers in July as simple common sense.
The fog does clear on some summer days, usually when the onshore flow weakens. That happens when the inland heat eases or the wind briefly turns offshore, which stops pushing marine air against the coast. Those days are often the warmest Half Moon Bay sees all summer, with highs in the mid 60s to low 70s and light wind. By coastal California standards, they are excellent beach days.
Fall: The Best Season on the Coast
September and October bring Half Moon Bay's most comfortable weather. The marine layer weakens as the North Pacific High shifts south and the contrast between the coast and the interior shrinks. Clear days become more common, and afternoons can reach 65 to 70°F with light wind. That kind of pleasant coastal weather rarely shows up during the July and August peak of the fog season.
The Half Moon Bay Art and Pumpkin Festival, held each October, falls during some of the sunniest weeks of the town's year. The pumpkin patches along Highway 92 fill with bright orange fruit. The hills stay golden until the first soaking rains turn them green, usually in November or December. For a few weeks, visitors see what the California coast looks like when the fog steps back.
Winter Rain and the Storm Season
In winter, Half Moon Bay sits directly in the path of Pacific storms. When atmospheric rivers and other storms reach the coast from November through March, the town takes the full force. It averages about 26 inches of rain a year, most of it in those months. In active winters, a single storm can bring several inches. Highway 1 occasionally floods or is blocked by landslides on the steep stretches along the coast.
Winter also brings a spectacular ocean. Large swells from distant Pacific storms travel thousands of miles to reach the San Mateo coast as powerful sets of waves. Mavericks, the famous big-wave break just north of town near Pillar Point, can produce wave faces of 40 to 60 feet on the biggest days. The water is no place for swimming in winter, and this stretch of coast is dangerous for anyone without cold-water training and gear. Distant tsunamis reach this exposed coast too. In 1960, the Chile tsunami raised the water about 7 feet in the Half Moon Bay area, far more than in San Francisco. Our guide to whether a tsunami can hit San Francisco covers the risk.
What the Weather Means for Visitors
If you are planning a day trip from elsewhere in the Bay Area, forget the inland forecast. A sunny 85-degree afternoon in San Jose often comes with thick fog and 58°F in Half Moon Bay, less than an hour's drive away. Always check the coastal forecast itself, and always bring a warm layer.
For sunny weather, the best times to visit are the shoulder seasons. May brings green hills, although fog is still common, and September and October bring the clearest days of the year. Clear winter days after a storm can also be beautiful. If you want the classic beach day of shorts and warm sand, Half Moon Bay will usually disappoint. For dramatic scenery, tide pools, the elephant seals at Año Nuevo or the raw power of the Pacific, the fog and cool air are part of the appeal. At low tide, the reef at Fitzgerald Marine Reserve north of town is a popular tide-pooling spot. Our guide to the best minus tides covers when to go.
