Guest Post by Ric Werme
The CSU Klotzbach/Gray Sep 1-14 hurricane forecast (PDF) is out. This period is the peak of the hurricane season and average conditions are pretty active:
“Climatology” is just the average weather, and “We expect that the next two weeks will be characterized by amounts of activity near (70 to 130 percent of) climatology.”
“Only” average, given that all eyes are on Earl, and a few more on Fiona? While Earl is racking up Accumulated Cyclone Energy (ACE) points now thanks to it being a category 4 storm, the NHC isn’t expecting new storm development, citing a high pressure system and dry Saharan air in the eastern Atlantic. Global models have no more storms in their forecasts.
This is not to say Earl and Fiona are it for the next two weeks, the total ACE expected from them is 15 units, but the forecast range is for between 20 and 37 units.
Another factor in tropical storm development is the Madden-Julian Oscillation, a band of enhanced and suppressed precipitation areas. Currently the oscillation is weak, as it was for the past two week period, so it will have little impact on storm development.
Overall, the expectations for an active season are balancing out the near term outlook:
The most recent seasonal forecast calls for a well above-average season. We utilize the seasonal forecast as a baseline for our two-week forecasts. Since the MJO is predicted to be weak over the next two weeks, and forecast models are not calling for much additional storm development over the next two weeks, we believe the next two weeks should have activity at near-average levels.
Finally, the two week period just ending came in at 250% of average. Klotzbach and Gray are only forecasting three ranges during the season, and they forecast activity would be “high,” or > 130% of the average. They credit the activity to low wind shear in the Main Development Region, but note that’s expected with warm Atlantic water and moderate La Niña conditions.