Florida precipitation and Niño 3.4 seasonal association

Research question

Does the historical rainfall–Niño 3.4 association differ by season?

Assess whether a public monthly Niño 3.4 sea-surface temperature anomaly index is associated with Florida statewide monthly precipitation, and whether the apparent relationship differs by season or a short Niño-leading lag. The comparison is fixed to one state, one index and the latest 40 complete calendar years, 1986–2025. It is an observational association, not a causal effect or a validated forecast.

Data and comparison design

The design keeps the 1986–2025 window fixed and distinguish the month-adjusted winter association from the direct winter-minus-summer contrast. A positive coefficient in one season is not by itself evidence that its coefficient differs from another season.

Input or source	Role in this case	Source context
NOAA PSL monthly Niño 3.4 anomalies	Public monthly SST index snapshot	Credit NOAA PSL; preserved text and hash in the Session ZIP; not the three-month ONI
NOAA NCEI Florida monthly precipitation	Public statewide precipitation snapshot	Credit NOAA NCEI; the saved source is broader than the selected 1986–2025 analysis period

Recorded findings

Winter analysis	Recorded result	Interpretation
Historical window	1986–2025	Supersedes retained 1950–2025 artifacts.
Contemporaneous slope	20.24 mm/month per 1°C Niño 3.4	Association with simultaneously observed climate conditions.
Pointwise 95% interval	13.73–26.60	Not the interval for the winter-minus-summer contrast.
Month-adjusted correlation	0.498	Neither a causal coefficient nor validated lead-time forecast skill.
Season contrast	Simultaneous interval includes zero	A positive winter association does not prove a winter/summer difference.

The corrected analysis uses 480 contiguous outcome months (40 years), with 120 monthly observations per season. The prespecified primary DJF lag-0 slope is 20.24 mm/month per 1°C higher Niño 3.4, with a pointwise 95% block-bootstrap interval of 13.73–26.60 and an approximate simultaneous interval of 10.35–30.13 mm/°C. The month-adjusted winter correlation is 0.498. The 11 direct contrasts and sensitivity results are in the corrected report and ZIP. In particular, the primary DJF-minus-JJA contrast's simultaneous interval includes zero; seasonal and lag comparisons should not be overstated. These are historical associations, not intervention effects or proof of forecast skill.

What the comparison shows

The winter association is clearer than the evidence for a seasonal difference. A contemporaneous association also cannot establish how well an operational advance forecast would work.

Assumptions and limits

These are historical associations, not causal effects or validated forecast skill. The simultaneous winter-minus-summer contrast interval includes zero. Climate dependence and modeling choices constrain inference; retained 1950–2025 artifacts are superseded.

Sources and research materials

The unchanged research package comes from upstream Case 20. It includes the archived session, analysis materials, results and figures. The poster uses an AI-generated illustrative photograph. This introduction summarizes archived findings; the analysis was not rerun.