Rain and Newport’s Extra Rise Before High Tide

In short: Rain can continue across a falling tide and into the next rise. On November 1st, 2026, that sequence preceded a Newport water-level pulse about 4½ inches above its already high pre-rain tide excess. The three other strong pulses also peaked on rising tides, one to two hours before predicted high tide. Rain crossed tide phases in storms without a strong pulse too. This pattern gives us a narrower time to watch, but four pulse events are not enough to forecast whether or how large the next pulse will be.

Rain can start while the tide is falling and continue into the next rise

The November 1 sequence is clear: rain began while the predicted tide was falling, then continued into the next rising tide before the extra-water pulse peaked. Corona del Mar first recorded rain at 7:55 p.m. PDT October 31. It recorded 0.43 inch during incoming-tide periods before the 2:55 a.m. PST November 1 pulse peak. Those times are 8 elapsed hours apart because daylight saving time ended overnight. The measured rain-and-tide overlap is a useful timing marker; whether the incoming tide slowed creek drainage still requires direct flow measurements.

The rain bars and curves illustrate one tide cycle; they are not measured November 1 values. In three shorter measured events, the pulse fell below the +2-inch study threshold about 1–2½ hours after predicted high tide. November 15 lasted much longer, and November 21 stayed elevated across two tide cycles. Event timing and tide-phase calculation.

All four strong pulses had measured local rain during a rising tide before the pulse peak. The pulse can also remain elevated through a falling tide and peak on the next rise, as it did on November 21, 2025. The tide phase of the first rain report or of a single weak maximum does not describe the whole storm. Creek-flow measurements at the bay mouth are unavailable to show exactly when rain-fed water arrived.

What happened on November 1?

The tide residual is the UC Davis water level minus NOAA’s predicted astronomical tide, using the same vertical reference. It was already averaging 25.05 inches during the 12 hours before the first rain report at SANC1 at Campus Drive in Orange County. Several five-minute readings exceeded 30 inches early on November 1. The highest was 33.1 inches. The largest moving one-hour average was 29.55 inches, a 4.50-inch rise above that pre-rain residual, centered near 2:55 a.m. PST. NOAA’s predicted high tide was at 4:05 a.m.

This figure starts its rain clock with SANC1 at Campus Drive’s first increment at 8:07 p.m. PDT October 31. The line uses fixed one-hour bins; the peak marker is the highest moving one-hour mean. Water calculations and chart code.

The one-hour rise stayed at least two inches above its pre-rain level for 4½ hours. Five-minute readings above 30 inches were intermittent between about 2:35 and 5:55 a.m. PST; the largest two-hour average was 28.5 inches, so there was no continuous two-hour average above 30. The first 12 hours after rain began averaged +1.64 inches, but the following 12 hours averaged −0.23 inch, relative to the pre-rain residual. The full 24-hour increase was only +0.70 inch. November 1 also had 25 clock hours because daylight saving time ended; all elapsed times here account for that change.

Which rain gauge best captures local rainfall?

SANC1 at Campus Drive in Orange County is near the upper bay and measures rainfall in one part of the watershed. The local comparison also includes Corona del Mar (CDMC1) and John Wayne Airport (SNA).

Corona del Mar recorded 0.78 inch, the creek 0.48 inch, and John Wayne Airport 0.04 inch during the November 1 storm. The right panel compares first measurable airport hourly reports, whose timestamps mark the end of an hour; airport traces can occur earlier. Local-gauge comparison, NWS November 1 storm report, and Orange County station record.

The NWS storm summary independently reports 0.78 inch at Corona del Mar and 0.60 inch at Costa Mesa by 7:02 a.m. November 1. The archived Corona del Mar counter first rose at 7:55 p.m. PDT October 31, just 12 minutes before the creek counter. The airport’s first measurable hourly report came nearly three hours later, although it had reported traces earlier. In two of the four pulse storms, its first measurable report came after the Newport water peak. Airport data alone would give the wrong impression of this local storm and a poor rain-onset clock.

Corona del Mar also covers the earlier events. Where its archive covers a storm, its first increment was within about an hour of the creek onset. The pulse classification and peak timing barely change when the clock starts there instead. The closer gauge changes the rain totals and confidence in local rain; it does not turn the pulse into a simple rain-total prediction.

What did earlier storms do?

The analysis compares ten selected rain episodes with Newport’s five-minute water readings and NOAA’s tide prediction. For each episode, it subtracts the preceding 12-hour mean residual, then calculates a moving one-hour mean. A strong sustained pulse is defined as a peak of +4 inches or more with at least one continuous hour above +2 inches. This is a comparison rule for this study, not a flood warning threshold. Four episodes met it; six did not. Corona del Mar data cover eight of the ten, including all four pulses.

Bars mark the continuous run above +2 inches, diamonds the largest one-hour rise, and ticks the following NOAA-predicted high. Dates name the peak day; rain sometimes started the day before. Recalculated local-gauge study and tide-phase check.

The next four charts show 60 hours around each storm’s first Corona del Mar rain increment. The top line pair is measured water and predicted tide. Orange bars show rain by elapsed hour; the orange line marks its first report. Teal shading marks the continuous one-hour residual rise above +2 inches, with a diamond at its peak. The gray dotted line marks the predicted high after that peak; an earlier high can also fall within the shaded run, as on November 21. All chart labels use Newport local time, including the November 2026 clock change.

November 15, 2025: only 0.04 inch fell in the first six hours, but the 24-hour total reached 1.85 inches. The +5.9-inch pulse peaked 18.7 hours after the first rain increment.

November 21, 2025: 0.63 inch fell on the first rising tide, 0.32 inch during the following fall, and 0.07 inch on the next rise. The residual was already elevated before the first high, stayed elevated through the fall, and peaked at +5.6 inches before the second high. Phase-by-phase audit.

December 24, 2025: the +5.0-inch pulse peaked at 9 a.m. on a rising tide. Of the 1.26-inch first-day total, 1.06 inches fell during the falling tide after about 10:50 a.m., while the strong residual was fading. Phase-by-phase audit.

November 1, 2026: 0.67 inch fell in the first six hours. The +4.6-inch pulse peaked 8.0 elapsed hours after first rain, ahead of high tide. Figure data and source checksums.

Those are four observed analogues, not a fitted distribution. They put pulse onset about 4½–14 hours after first local rain, the strongest hour about 8–19 hours after it, and the sustained run at 4½–19 hours. The November 1 peak is about 8.0 hours after Corona del Mar’s first increment, rather than 7.8 hours after the creek’s. Shifting the pre-rain baseline from 12 to 24 hours changes the four peak rises by about 0.2–1.1 inches but leaves all four above the strong-pulse threshold. Duration is less stable: using a two-hour moving mean extends November 15’s run from 19 to about 31 hours; the other three change by less than an hour. The one-hour definition stays consistent across events.

Can rain amount predict the pulse?

The closest comparison is striking. Corona del Mar measured 0.78 inch in the first 24 hours of the November 1 storm and 0.79 inch on December 26, 2025. November 1 produced a +4.6-inch peak one-hour pulse; December 26 reached only +1.4 inches. A threshold based on local rain total would have treated them nearly alike. December 26 was also not a case of rain confined to a falling tide: 0.67 inch fell on the first rise, 0.08 inch on the fall, and 0.04 inch on the next rise. Neither rise produced a strong pulse. Full rain-and-tide sequence.

Eight episodes have Corona del Mar coverage; filled points are the four strong pulses. Each 24-hour rain window starts with that gauge’s first increment. Some rain fell after the water peak, so the completed total is a retrospective comparison, not an advance forecast input. Underlying comparisons.

Across those eight events, first-six-hour Corona del Mar rain had almost no useful ranking power for the later pulse (AUC 0.38, where 0.5 is chance). The completed 24-hour amount ranked pulses better (AUC 0.88; correlation with peak rise 0.71), but it uses rain that may fall after the peak. Corona del Mar and the creek broadly agreed on their same-window 24-hour storm totals (correlation 0.96); the airport’s totals had a much weaker relationship with Newport’s pulse size (correlation 0.24). With only eight locally covered events, these correlations are clues, not a calibrated forecast equation. Hourly rain across the watershed can set the watch clock; Newport’s live residual can show whether a pulse is actually growing.

Is the incoming tide part of it?

The first Corona del Mar rain increment was on a falling tide for November 15, 2025 and November 1, 2026, and on a rising tide for November 21 and December 24, 2025. Rain reached a rising tide before the peak in all four strong events. But among the eight storms with local-gauge coverage, all eight had some rain on both rising and falling tides. That overlap alone cannot separate the four strong pulses from the four weaker events. December 26 even had nearly the same first-day rain as November 1, including rain on two rising tides, without a comparable pulse. January 1 had 0.74 inch on rising tides and a peak rise of only +1.9 inches. Phase-by-phase audit.

November 21 shows what the timing pattern can narrow. Its one-hour residual rose to about +4.0 inches during the first incoming tide, stayed around +2–4 inches as that tide fell, then reached +5.6 inches on the next incoming tide. December 24 shows a different sequence: the strong pulse peaked on the morning rise, then weakened while most of that day’s rain fell during the subsequent fall. The phase of one selected maximum misses both stories. The repeatable feature in the four strong cases is the strongest hour occurring roughly one to two hours before a predicted high, not a requirement that every raindrop fall on a rising tide. These are measured associations, not proof that the incoming tide caused the extra residual.

A physical interaction is plausible. UC Davis describes runoff and tide meeting in Newport Bay, and the Army Corps reports tidal influence up San Diego Creek toward Campus Drive. An incoming tide might slow drainage or change where runoff pools. But at the November 1 peak, independent Los Angeles and San Diego tide residuals had also risen about 2½ inches from their pre-rain levels, against 4½ inches at Newport. The remaining difference cannot be assigned to creek backwater without downstream flow and more bay gauges. The matched dry windows also have overlapping samples, so their tide-phase contrast is suggestive rather than a causal test. Phase analysis.

Which tide matters for the next rain?

The NWS discussion issued 4:27 a.m. PST November 6 says late-week rain is uncertain. About 52% of its Thursday ensemble scenarios remain dry locally; the others allow at least weak troughing and a slight chance of rain. For Friday, its general consensus is light precipitation, if any, despite a wider range of possible weather patterns. This does not establish heavy rain on November 15. A retained single long-range ECMWF-based run has only about 0.19 inch of coastal rain between 11 a.m. and 4 p.m. Saturday November 14, about 0.02 inch at its lower-watershed grid point, and almost none on November 15. That is one model run, not a storm forecast for the whole watershed. Retained NWS discussion.

Two different scenarios: the 8:50–9:50 a.m. peak watch applies only if meaningful rain starts Friday evening. One long-range run instead puts light coastal rain after Saturday’s 10:52 a.m. predicted high. The NWS outlook does not specify an hourly rain onset. NOAA tide predictions, forecast snapshot, and chart sources.

The rain clock starts at the first credible Corona del Mar or SANC1 increment. The four strong-event peaks occurred 8–19 hours later. A more focused conditional peak watch is the one to two hours before each predicted high roughly 9–21 hours after first local rain. If rain or an elevated residual carries through a falling tide, the next incoming tide remains a candidate; November 21’s strongest hour came on that second rise. A weak maximum during a fall does not close the watch while rain continues. These tide windows narrow the clock but cannot predict that a pulse will occur: December 26 and January 1 also had rain on rising tides without a strong pulse. Timing audit and peak phase check.

If a strong pulse develops, the four analogues put its strongest one-hour mean at +4.6–5.9 inches above the pre-rain residual, with a run above +2 inches lasting 4½–19 hours. Total water level is forecast as predicted tide plus an updated residual, with the pulse represented inside that residual. Adding the analogue rise again to a storm-adjusted water forecast would count some water twice. Newport’s live one-hour residual should replace the analogue estimate as readings arrive. A future fitted model should test rain totals separately for each rising and falling tide, recent rain intensity, and the observed residual trend across many more storms.

These starts are scenarios, not an hourly NWS forecast. Each row gives one candidate high; it does not exclude a prior rise or a later one if rain and an elevated residual continue across the tide turn. November 21 began rising before its first high and reached its strongest hour before the second. If meaningful rain starts late Friday, the most focused conditional peak watch is Saturday November 14, 8:50–9:50 a.m., ahead of the 10:52 a.m. 4.89-foot MLLW high tide. Earlier rain shifts the focus toward the preceding nighttime highs. If the lighter Saturday model run is closer, a strong rain-driven pulse is not the central expectation, and its historical peak window misses Sunday’s daytime high.

A November 1-style pulse is not forecast for November 15 on the current light-rain outlook. If a more substantial Thursday–Friday storm develops, the provisional peak watch spans November 12 afternoon through November 14 midday, narrowed to the one-to-two-hour windows before qualifying predicted highs once local rain timing is known. Meaningful rain delayed until Saturday would shift the broad conditional watch into Saturday night–Sunday morning; the four analogues do not identify a strong-pulse high in that branch. If a pulse does develop, their observed bounds suggest a roughly +4–6-inch peak one-hour rise above the measured pre-rain residual and a roughly 5–19-hour elevated run. Those bounds come from four selected events and may not contain the next one. The useful next update is the hourly local rain onset forecast, followed by Newport’s live one-hour residual as rain arrives.

How to stay informed

Follow @nbflood on Instagram for updates as the next rain approaches. When forecast local rain is expected to continue into a rising tide within the historical watch window, we will post the expected rain timing, the high tide to watch, and when an extra water-level pulse might peak. We will update those posts as local rain reports and Newport’s measured water level come in, including any sign that a high tide could run above the tide-only prediction. The four strong events help narrow the watch time; they do not yet tell us whether a pulse will occur or exactly how high it will reach.

Follow the current water level and forecast on the NBFlood tide charts, and check upcoming astronomical highs in NOAA’s Newport Bay Entrance predictions. If the rain and tide timing line up, look to Instagram for frequent updates as the watch changes.