Update: as of 5 pm, Hurricane Bertha has continued to intensify and has reached 100 knots or Category 3 on the Saffir Simpson scale. NHC Discussion
BERTHA’S INTENSIFICATION TO MAJOR HURRICANE TODAY HIGHLIGHTS THE
DIFFICULTIES OF FORECASTING RAPID INTENSITY CHANGES.
The HWRF model has been the winner so far, correctly predicting Major hurricane status yesterday.
Yesterdays HWRF model at 06Z:
Bertha developed an eye overnight and was upgraded to hurricane strength this morning. The gradual but persistent intensification over the past several days will likely continue for another 72 hours until Bertha reaches cooler waters and less hospitable atmospheric shear.
Image: HWRF 126 hour wind speed forecast swath for July 7, 2008.
The storm is forecast to recurve out to sea and not bother land.
July hurricanes in the far Atlantic basin are rare. However, coincidentally, in 1996, Hurricane Bertha developed on July 7 as well and made landfall in North Carolina. Bertha tracked further south and encountered much warmer water allowing it to intensify to major hurricane status.
Bertha 1996 (wikipedia.org track)
There is no evidence and no one can make a scientifically honest statement that this storm’s strength is in any way related to global warming. Yet, it bears watching how the media and political scientists/opportunists will interpret this natural event.
Tropical Storm Bertha is continuing to race westward and slowly strengthen. As of the 11 pm advisory, Bertha’s maximum sustained winds were at 55 knots, just below the 64 knot threshold for hurricane strength. The satellite appearance has improved markedly with a burst of strong central convection.
A key to understanding Bertha’s intensity is the warmth or amount of fuel available in the ocean surface layer. The “heat content” map shows the track of Bertha towards a more favorable environment for intensification. However, it is still July, and there is a definite cap on maximum intensity possible, which would be at just under 100 knots or Category 3 strength. This would require perfect atmospheric conditions including very low shear but high relative humidity or “juice”. The likelihood of a US landfall is very low at this point in time, but not zero.