When a storm is active in the Atlantic, the latest and greatest hurricane forecasts from the National Hurricane Center get almost all of the attention, whether from media, enthusiasts or other meteorologists.
However, the most “current” forecast doesn’t always tell the full story. The Hurricane Center doesn’t like to make big forecast track shifts from advisory to advisory when large changes in model guidance occur. For example, if the models shift from a recurving system to one that moves 20 degrees further west in a 6 hour forecast cycle, the NHC will gradually make track adjustments to reflect the trend over several forecasts. This is to ensure forecast tracks don’t “windshield-wiper” between forecasts.
Remember, their goal is simple…minimize track and intensity forecast errors. They have learned “flip-flopping” causes higher forecast errors, and there is value in persistence.
The above graphic is a longer-term view of the 5 day NHC forecast tracks issued for Sandy, with lighter colors representing the early forecasts, gradually becoming darker over time (latest forecast is the darkest shade of blue).
This analysis can reveal the longer term forecast thinking, either in real-time (how are trends changing) or in retrospect. In this example, notice how the early forecasts (lighter paths) had an easterly bias, reflecting the early model trends of recurving Sandy in most of the models.
However, notice how tightly clustered these forecasts were when Sandy bent back toward the US east coast. That tight grouping showed the confidence they had over many forecast cycles. By that time, Sandy was very well-behaved, and the model guidance was consistently showing an east coast landfall.
I am considering making these type of graphics/products available during the 2013 Atlantic hurricane season, updated after each advisory is issued.
Please feel free to pass along any comments or questions about this graphic.