Original readings of archived official bulletins, not accounts of a voyage we sailed and not a forecast-accuracy backtest. Dates below are historical; none describes current conditions.
Beryl: one system, several different warning layers
At 15:00 UTC on 2 July 2024, NHC public advisory 16 listed a hurricane warning for Jamaica, a hurricane watch for the Cayman Islands and southern Haiti, and other distinct coastal messages. The narrative also addressed swell away from the centre.
Decision exercise: a planned island leg must identify the warning type, coast, timing and next advisory separately. A forecast point away from the centre cannot clear that leg. Save the advisory number, map each relevant warning to the leg, obtain the local marine bulletin and record what new information would change the plan. The next full advisory in that archive was scheduled for 21:00 UTC; that is a refresh appointment, not a promise of unchanged conditions until then.
What this proves: the layers and update schedule in this particular advisory. What it does not prove: a safe alternative track, sheltered harbour, conditions at an unobserved boat position or performance of a weather app.
Franklin: no coastal warning does not mean no swell hazard
NHC advisory 23, 26 August 2023 at 09:00 UTC, listed no coastal watches or warnings, yet described expected dangerous swell affecting Bermuda and advised consultation of the local weather office. The subsequent advisory 30, 28 August at 03:00 UTC, described swell affecting Bermuda and spreading toward the US east coast.
Decision exercise: do not reduce a report to a binary warning badge. For an approach, add swell period/direction, harbour orientation, breaking-sea exposure and the local service’s current bulletin. Record missing data as unresolved, not as zero risk. A modest local wind field cannot rule out remote swell.
What this proves: the hazards communicated in the archived advisories changed over time and were not equivalent to the coastal-warning field. It is not a reconstruction of every sea state or a recommendation for a real departure.
A repeatable way to study a decision
- Freeze the evidence that was available at the decision time, with UTC and bulletin numbers.
- Write the intended leg and ETA assumptions; separate known facts from hypotheses.
- Record the chosen refresh time and specific triggers; then examine the next issued evidence.
- Use later observations to assess the forecast separately. Do not use hindsight to claim that an unvalidated route was safe.
Editorial analysis: 26 September 2026. Archive sources: NOAA/NHC.
Evaluate the decision without hindsight
Use two columns: evidence available at the decision time and evidence issued afterwards. First record what the earlier information could and could not establish; only then inspect later advisories. A fortunate outcome does not prove the original decision was well supported, and a later track change does not prove the previous forecast was useless.
A reusable case-study record
Keep archive URLs and bulletin numbers, issue/valid UTC, the assumed route and ETA range, decision-changing hazards, missing evidence, next scheduled check and why the plan changed. To assess forecast accuracy, add suitable independent observations as a separate exercise. These cases illustrate evidence handling; they are not a claim that we sailed the passages or validated an avoidance route.
Editorial review of this material: 27 September 2026. This date concerns the page content; check current forecast issue times and validity at the original sources.