Tropical Storm/Hurricane Elsa finally cleared Florida on Thursday after over a week of waiting and impacts. Elsa was a rare early season Cape Verde-type storm which made its forecasting particularly difficult and unique.
The National Hurricane Center (NHC) did very well in projecting a forecast track – remarkably well in fact. The modeling that the NHC uses particularly the GFS model were deadly accurate for over a week projecting a track of over 1,000 miles. This is remarkable by any standard.
What was frustrating was the poor intensity forecasting of the modeling and NHC on the storm. Intensity forecasting unlike directional forecasting remains incredibly challenging – we just don’t have the scientific tools yet to accurately forecast every little elements of tropical systems.
In the case of Elsa, the storm twice intensified to Hurricane strength at a time when most of the modeling as well as the NHC forecast had it remaining a Tropical Storm at the time and similarly remained a Tropical Storm on an occasion when it was supposed to intensify to a Hurricane.
At various times models had a wide variation as to forecast intensity.At one point on of the NHC member models had the storm reaching Category 3 strength when entering the Gulf of Mexico which while an outlier had to be factored into forecasting. Another model, the British UKMET model had Elsa weakening to depression strength around Cuba (which by the way wasn’t as crazy as it seemed, since Elsa did weaken substantially at this point, but not quite to depression strength and was again a Hurricane the next day).
However, the overall takeaway is positive. Take a look at the above model runs from when Elsa first achieved Tropical Storm status east of the Leeward Islands. The 120 hour forecasting here in terms of direction and path are remarkable.Throughout the week these forecast paths stayed remarkably similar and even when wobbles in the storm or eye replacement cycles occured, the NHC was able to nail the general direction of the storm without much difficulty.
Cape Verde-type storms this time of year are very rare and Elsa somehow survived the journey across the Atlantic despite Sahara dust, unfavorable water temperatures and other atmospheric factors such as dry air and wind shear that limit development of June and July storms.
The storm’s remarkable journey gives us insight into forecasting and atmospheric conditions for the remainder of the Hurricane season which runs through November but peaks in August and September.