Background: Otitis externa (OE) is a common, painful inflammatory condition of the external ear canal, with incidence influenced by environmental factors. While seasonal variation is accepted, state-level data quantifying this in Australia is lacking. Ototopical antibiotic drop prescriptions serve as a robust surrogate indicator for OE incidence. Objectives: This study aims to 1) quantify seasonal OE incidence across Australian states and 2) identify the specific climate drivers (temperature, humidity) by modeling their relationship with prescription volumes. Methods: Publicly available PBS prescription data (2004-2024) were aggregated by month and state. Monthly climate data (high temperature, humidity) were matched to prescription volumes. Analysis involved Kruskal-Wallis tests for seasonality and Multiple Linear Regression (MLR) models, stratified by climate zone (Temperate vs. Tropical/Hot). Results: A significant seasonal variation was observed, peaking in Summer, but this pattern varied by state. QLD and NSW showed strong seasonality (p<0.0001), while VIC and TAS showed none (p>0.99). The MLR analysis explained this divergence. In Temperate states, a weak but significant relationship was found (Adj. R²=.111, p=.027), driven by both High Temperature (p=.010) and Humidity (p=.011). Conversely, in Tropical/Hot states, the model was stronger (Adj. R²=.239, p=.001) and driven almost exclusively by High Temperature (p<.001). Conclusion: Ototopical prescriptions are an effective surrogate for OE. The observed seasonal pattern is not uniform but is quantifiably driven by distinct climate factors that vary by region. In temperate zones, OE is weakly associated with both heat and humidity. In tropical/hot zones, incidence is strongly and independently driven by high temperature alone. This provides a data-driven basis for region-specific public health preparedness.