During the 2015 Atlantic hurricane season, this blog will focus on tropical systems that impact The Bahamas and Turks & Caicos Islands.
By: BahaHurican, 3:37 PM GMT on July 10, 2008
I just looked back at the Bertha graphics archive. It's interesting to note that Bertha crossed 55W at almost exactly the location on Tuesday that NHC had forecasted she would the previous Thursday (while Bertha was still a tropical depression). This was the very first advisory they did, and they seemed to have nailed the 5-day track on that one.
I must say that NHC track forecasting ability has really improved in the years since the introduction of satellite technology, and particularly since 2003, when they have had numerous opportunities to apply skills and tweak tools. It is true that storms like the early Katrina and the late Charley still create problems with forecasting rapid intensification and short-term motion, and intensity forecasts on the whole still present NHC with some serious challenges. Nevertheless, the long-range forecasts have become much more sophisticated and accurate.
To put this into perspective, the other night fellow blogger lefty420 and I had a disagreement because he felt I was comparing NHC forecasting for Hurricane Betsy of September 1965 with current forecasting.
For those who may not recall, Betsy was a Category 4 storm that bypassed the southeastern Bahamas on its way northwest (similar to Bertha's track, only further west), apparently headed for the Outer Banks of North Carolina. East of Cape Canaveral it made a loop and, following an unusual southwest track, struck first the northern Bahamas, then Southern Florida. Betsy went on to flood New Orleans and devastate the Louisiana coast.
I had brought Betsy up not because of the forecasting but because I wanted to illustrate the unexpected paths that storms can take and also because I was speculating on the weather conditions that must have been in place to force such a track on a powerful hurricane. (I was also illustrating why some of the hurricane "veterans" won't dismiss any storm as a "fish" until it's dissipated).
However, lefty's point was a good one; in 1965, NHC forecasters were astounded (and probably horrified) to observe Betsy make an anti-cyclonic loop and head south. Talk about a forecast that did not verify! In 2008, given the wide array of tools available to NHC personnel (and to a lesser extent the weather-fascinated public) not only would Betsy's unusual behaviour have been anticipated, it's likely to have been forecast at least three days, and possibly up to five days, in advance. At least SOME of the models would have suggested it.
More importantly, better ability to observe and forecast larger trends in weather - movement of high and low pressure systems - along with a better understanding of how these movements impact and are impacted by tropical storms - means that NHC personnel are more likely to interpret data correctly and make forecasts that take the many different variables into account. As a result, when Hurricane Jeanne made a similar loop in a similar location in 2004, NHC forecasters were not caught off-guard. While the forecasts for Jeanne were not spectacularly good, the loop was anticipated, and Bahamians and Floridians had more notice to prepare themselves for Jeanne's turn.
Since Bertha's formation on 3rd July, 2008, NHC's discussions have included numerous comments about the uncertainties connected with Bertha's forecast. Yet it is undeniable that these forecasts, seemingly doubtful, have also been very skillful indeed.
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.