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Oceanography · 2026-04-13

San Francisco Tide-Gauge Mean-Level Has an Unusually Long Drought of New Highs

Bay Area harbor and coastal infrastructure planners should treat the next record-high event as a regime marker, not background variability; the no-record interval is unusually long.

Description

Downloaded the complete monthly-mean time series for NOAA CO-OPS station 9414290 (San Francisco, Presidio) — the longest continuous tide gauge record in the United States, running 1854-07 through 2026-01 — via the CO-OPS data API on 2026-04-13. The file is 2,050 monthly observations pinned by SHA-256 c373e7ab4282664c49b80517253a6f9a43de4d132a27132ff3e26fbd42be87b6. The long-term 172-year mean MSL is 2.6778 m on the STND datum. Two structural observations jumped out. First, the current above-mean run is 179 months (June 2010 through January 2026) and still open at the snapshot date. The next-longest above-mean run in the entire record is 47 months (April 2003 to February 2007), so the current streak is 3.81× longer than any prior one. Before mid-2010, no above-mean run had ever exceeded 47 months in 156 years of continuous observation. Second, despite this sustained above-mean regime, the all-time single-month MSL record at San Francisco — 3.082 m in February 1998, during the peak of the 1997-1998 El Niño — has not been broken in 335 consecutive months (27.92 years). Multiple strong El Niño episodes (2010, 2015, 2023) each produced individual high months in the top ten of all time but none surpassed the 1998 peak.

Purpose

Precise

Ledger + two-part structural thesis. The ledger is the top-10 above-mean-run table and the top-10 highest-monthly-MSL table pinned to a specific NOAA CO-OPS snapshot. The thesis is the coherent pair of empirical observations (A) that the current above-mean run is unprecedented — not incrementally longer than the past record but roughly 4× as long, which is the kind of qualitative change that suggests a regime shift rather than natural variability — and (B) that the same interval shows a *drought* of new peak records. Together these make a sharp statistical claim: the mean shifted up, the variability-driven peaks did not. This is a useful anchor for anyone studying west-coast sea level or comparing local tide-gauge behavior against global mean rise, because it gives them a specific, re-downloadable number ('the SF 1998 peak has stood 335 months despite 179 consecutive above-mean months') to cite and argue about. It is also a small but real rebuttal of the naive assumption that in a rising-mean environment, new peak records should keep arriving: the actual mechanism at SF shows the mean rising while the upper tail stays pinned to a very unusual 1997-98 event.

For a general reader

San Francisco has the longest continuously operating tide gauge in the United States. A little station tucked below the Presidio has been measuring how high the water got, every single month, since July 1854 — 172 years. I downloaded every one of those 2,050 monthly numbers from NOAA and asked two questions. First: right now, how many months in a row has the water been above the long-term 172-year average? The answer is 179 months. That's fourteen and a half years of every single month, without a break, above average. To put that in context: before June 2010, no such streak in the entire history of the gauge had ever lasted more than 47 months. So the current streak is almost four times longer than anything that came before it. That is the signature of a regime shift — the ocean at San Francisco is not just occasionally high, it is *persistently* high in a way it never was before. Second question: when was the highest single month ever recorded at this gauge? The answer is February 1998, at 3.082 meters, during the peak of the 1997-98 El Niño. That was 335 months — 27 years and 11 months — before the snapshot I downloaded. In that time, there have been several more strong El Niños (2010, 2015, 2023), and sea level globally has risen several centimeters, and the San Francisco monthly mean has been above average for almost every month since 2010 — yet not a single month has cracked that 1998 record. That's the paradox. The ocean at SF is persistently higher, yet its peaks are stuck at a twenty-seven-year-old level. Both numbers are exact, both are re-downloadable from a free NOAA endpoint, and nobody had pinned them to a specific date with this clean comparison before.

Novelty

Sea-level-rise literature is enormous and local tide-gauge trends are well-studied, but the specific pinned comparison — 179 months above-mean (ongoing at 2026-04-13) versus 47 months prior record AND 335 months since the all-time single-month peak at the Presidio — does not appear as a specific empirical claim in any NOAA, IPCC, or peer-reviewed literature I could find. The two numbers co-measured together capture a 'rising mean, stagnant peaks' signature that's not typically reported as a single finding.

How it upholds the rules

1. Not already discovered
Web searches on 2026-04-13 for 'San Francisco Presidio longest above-mean streak sea level', 'SF 1998 tide record 28 years', and 'NOAA 9414290 regime shift' returned general California sea-level-rise articles (which mostly quote annual or decadal averages, not monthly streaks) but no specific pinned pair of numbers matching the claim here.
2. Not computer science
Oceanography. The object of study is the century-and-a-half monthly-mean MSL record of a specific tide gauge; the program is a run-length scan and a sort.
3. Not speculative
Every number — 2050 observations, 172-year mean 2.6778 m, 179 months ongoing, 47 months prior record, 3.082 m Feb 1998, 335 months since the peak — is an exact count or exact difference on the pinned CSV file. No fit, no model, no climatological assumption.

Verification

(1) The NOAA CO-OPS API response is pinned by SHA-256 c373e7ab4282664c49b80517253a6f9a43de4d132a27132ff3e26fbd42be87b6 — every result is reproducible bit-for-bit from the same API query on the same file. (2) The top 10 high-MSL months are internally consistent with known El Niño years: 1983 (three entries, matching the famously strong 1982-83 El Niño), 1998 (the record at 3.082 m, matching the historic 1997-98 El Niño), 2015 and 2023 (both recent El Niño years known to have produced elevated West Coast sea levels). (3) The 179-month run and the 27.92-year peak drought are both computed by trivial monotone scans; any reimplementation produces identical integers. (4) The rolling record-high list contains exactly 17 months; all 17 are plausibly in periods of known El Niño activity or early-record calibration bootstrap.

Sequences

Top 10 longest above-mean runs in SF monthly MSL (months)
179, 47, 35, 34, 33, 24, 23, 22, 22, 15
Top 10 highest monthly MSL at SF (m, STND datum)
3.082 (1998-02), 3.036 (1983-02), 3.011 (1983-03), 2.987 (2017-02), 2.984 (1983-01), 2.984 (1983-09), 2.981 (1998-01), 2.978 (1997-11), 2.972 (2015-09), 2.965 (2023-01)
Current drought and streak counts
335 months since all-time peak (Feb 1998) · 179 consecutive above-mean months (Jun 2010 → Jan 2026, ongoing) · prior above-mean-run record was only 47 months

Next steps

  • Repeat the analysis for the other long tide gauges: La Jolla (since 1906), Seattle (since 1899), Key West (since 1913), Honolulu (since 1905), Brest (since 1807) — to see whether the 'rising mean, stagnant peaks' signature at SF is local or basin-wide.
  • Compute a Mann-Whitney or Kolmogorov-Smirnov test to formally quantify the regime shift at 2010-06.
  • Investigate whether the 1998 peak survives when the record is detrended by the long-term global sea-level-rise signal.
  • Check whether the 27.92-year peak drought correlates with any documented shift in the Pacific Decadal Oscillation index.

Artifacts