Why Summer's Lowest Tides Happen at Dawn on the Pacific Coast

Pacific-coast tides have unequal daily lows, with the deeper summer low tending toward daytime. Across Tidewindow's 11 western stations, July 1–December 31, 2026 NOAA predictions contain 953 minus tides; 548 surrounding windows overlap daylight by at least 30 minutes. The busiest low-time hour is 6 AM (58 windows), not a guarantee of daylight at low water. Seattle's deepest qualifying low in this period was predicted for July 14 at 11:20 AM, −3.80 ft (NOAA 9447130).

If you keep one explanation, keep this one:

Pacific coast tides are mixed semidiurnal: two low tides a day, one much lower than the other, and how far the moon and sun sit north or south of the equator decides which one that is. In summer the geometry parks the deep low in daylight; in winter the same deep low happens at night.

The rest of this page is the supporting evidence, straight from NOAA's harmonic predictions.

Why does the West Coast get two different low tides a day?

The Pacific coast runs on what NOAA calls a mixed semidiurnal tidal cycle: "two high and two low tides of different size every lunar day." A lunar day is 24 hours and 50 minutes, the time it takes a point on Earth to rotate back under the moon, which is why everything in a tide table drifts about 50 minutes later each day.

The "different size" clause is the part that matters. On most West Coast days one low is unremarkable and the other is much lower, and only the lower one is a candidate for a minus tide (a low below 0.0 ft MLLW). So "when is low tide?" is really two questions on this coast, and only one of the two answers can put bare reef in front of you.

How does declination decide which low goes deep, and when?

Declination is the angle of the moon or sun north or south of Earth's equator. When the moon stands off the equator, NOAA's tide-physics primer explains, "the tidal force envelope produced by the moon is canted." Tilt the envelope and the two daily tides stop matching: as Earth rotates, your beach sweeps through a deep part of one tidal bulge and a shallow part of the other. That mismatch is the unequal-lows pattern above. The moon crosses the equator twice each month, so the inequality swells and shrinks on a monthly rhythm.

The sun runs the same geometry on a yearly clock. Near the June and December solstices, the sun reaches "its maximum declination, i.e., its largest angle to the equator" — a line NOAA's declination page quotes from Sumich's 1996 marine-science text. And around new and full moon, NOAA notes, the solar tide "has an additive effect on the lunar tide" — the spring tides that deepen lows roughly twice a month.

Put the monthly clock and the yearly clock together and you get the seasonal schedule. The University of Washington's LiveOcean tide primer describes the Pacific Northwest pattern: lower low water tends to occur in daytime in summer and at night in winter, linked to Earth's axial tilt relative to the sun. That is a seasonal tendency, not a substitute for checking a particular station and date.

What does the July–December 2026 data actually show?

This is a partial-year sample, not an annual total: July 1–December 31, 2026, inclusive in each station's local date, including past and future dates. NOAA predictions give the 11 West Coast stations 953 minus tides. Of those, 548 (58%) have a modeled below-+1-ft-MLLW window that overlaps sunrise-to-sunset daylight by at least 30 minutes. The low itself can occur before sunrise or after sunset; qualification does not confirm beach access.

Here is the low's local clock hour for those 548 qualifying windows. Each hour bin includes its full hour (the 9 AM bin runs through 9:59 AM):

Recomputed 2026-09-27 from NOAA predictions at Tidewindow's 11 West Coast stations (WA, OR, CA), July 1–December 31. The original July 3 snapshot omitted 13 early-July minus tides, all qualifying: July 1 at all 11 stations plus July 2 at La Jolla and San Diego. Thus 940 + 13 = 953 minus tides, and 535 + 13 = 548 qualifying windows.

The shape has a morning hump and another late in the day. The 6 AM hour has 58 qualifying windows, versus 12 apiece at 11 AM and noon. The 3–9 AM hour bins contain 280 of 548 (51%); the late-day peak is 51 at 5 PM. These are clock times across the July–December sample, not a summer-only histogram or a claim that every low occurs in daylight. Explore a station's seasonal pattern on the year heatmap.

What does a summer run look like at one station?

Seattle, NOAA station 9447130, makes a clean historical example. These six July days have now passed; each predicted low itself fell between sunrise and sunset:

Re-verified 2026-09-27 from NOAA station 9447130 (Seattle) predictions. The historical heights and times are unchanged. The full month is on the July 2026 calendar; arrive-by times are calculated planning offsets, not confirmation of shore access.

Read down the time column: 8:49, 9:40, 10:31, 11:20, 12:08, 12:55. Each low is 47 to 51 minutes later than the previous day's — the lunar day's roughly 50-minute lag, visible in a tide table. Over six days the predicted low moved from mid-morning to just past lunch while deepening to -3.80 ft on July 14, Seattle's deepest qualifying low in the July–December sample. This example also shows why "summer morning" does not mean every low is at dawn. The Tide Window Finder checks upcoming dates and calculates arrive-by times.

Where do the deep lows go in winter?

They still occur, but in Seattle the qualifying daylight overlap disappears. This station's July–December comparison separates modeled below-+1-ft windows from the stricter minus-tide subset with at least 30 minutes of window/daylight overlap:

Recomputed 2026-09-27 from NOAA station 9447130 (Seattle) predictions; complete July–December station-local months. The middle column counts resolved windows in Tidewindow's model, not every predicted low below the threshold: very brief or unresolved dips can be omitted.

October has 20 modeled below-+1-ft windows versus July's 24, but no qualifying minus-tide window versus July's 20. November and December each have 21 modeled windows and no qualifying minus windows. That result is specific to Seattle; other Pacific stations can retain daylight-overlap windows in winter. The seasonal shift in the deeper low and shorter days both matter. For the high-water side, see the king tide schedule. The daylight-minus-tide index offers a separate rolling-year station comparison, not this fixed July–December sample.

The practical summary is unromantic: start with morning predictions for a summer trip, then check the actual station, date, daylight and access. The methodology page documents how each window in these counts is defined and scored. A seasonal tendency helps narrow the search; it does not set the appointment.