In short
Different models and presentation — disagreement is normal.
Different sites ingest different models, update on different schedules, and draw maps with different smoothing.
Two well calculated forecasts can disagree by several knots or an hour of sea-breeze timing.
It's the nature of weather. Who said all forecasts should agree? Forecasts for Property, Interest Rates and Hair Styles differ - there is no one source that is always right, but somehow, many people believe that.
