THE BENCHMARK METHOD – MATTHEW
The benchmark method in hurricane forecasting is a little known but extremely useful technique when there is a great deal of model uncertainty which is the case with hurricane Matthew. The benchmark method uses hurricane models global models and also the climatology. It is based on the idea of building scenarios or possibilities based upon benchmarks or important key positions based upon geography and the current upper air patterns.
In order to use the benchmark method correctly the forecaster has to understand the uncertainty or the variable IS
In this case the Uncertainty is WHERE will hurricane Matthew be located when it crosses from the Caribbean into the southwest Atlantic in the Bahamas. ? Obviously the further west into the Bahamas hurricane Matthew tracks ...the bigger the threat will be to the southeast US coast.
And conversely the further east hurricane Matthew will be when it reaches the Bahamas... the chances of seeing some sort of Southeast US coast impact would be significantly less
I want to make a point by BEFORE the new model data started coming out. This 1ST IMAGE shows the shift in the official NHC of the track of hurricane Matthew from 11:00 AM on Thursday to 5:00 PM on Friday.
The reason however that I am showing this shift this has to do with IMAGE #2 which I issued on Thursday on the2 weekend newsletter and on the DTVaWeatherman Twitter account. We tried to make it clear that in our view the key was going to be when Matthew was going to turn North and WHERE hurricane Matthew would cross over from the Caribbean into the Bahamas. We saw three possible paths. --
the BROWN track was taking Matthew over Jamaica and into central and eastern Cuba. This would mean that Matthew would end up into the Western Bahamas which increases the threat of a landfall Ian floor at or the southeastern U.S. The GFS model as well as many of the GFS ensembles have been showing this sort of track for the last several days.
The BLUE track was the official NHC track which took hurricane Matthew just to the east of the far eastern tip of Jamaica and across far Eastern Cuba into the Central Bahamas. From there it would pose some sort of threat to the southeastern U.S. IF...IF ... hurricane Matthew would turn back to the northwest for 2 days and towards the Carolina Coast.
The GREEN solution was the most easternmost solution which just happened to be the European model. In this solution hurricane Matthew would cross Western Haiti and move into the Eastern Bahamas. This would reduce the threat of US landfall from hurricane Matthew to any portion of the southeast US coast because the Hurricane would be so far off the coast that it would take a huge shift to the Northwest to drive Matthew back towards the SC NC Coast.
By using the benchmark method forecasters can develop several possibilities and then watch how the model data rules in and see where the shifts are a current. This enables the forecasted a stay ahead of the game and not get overwhelmedby shifting model data and tracks