Early last week I discussed the potential for the development of Tropical Storm Bonnie later in the week.  Long-range models correctly predicted the increasing thunderstorm activity across the tropics the second and third week of July, which did lead to the development of Tropical Storm Bonnie.  Fortunately, Bonnie formed very near a large upper-level low pressure system which helped to keep its intensity in check. So the models did a fair job in at least identifying that the conditions would be suitable for development last week.

We can often follow pulses of increased tropical activity starting in the Indian Ocean, progressing eastward across the West Pacific and eventually reaching all the way to the Atlantic Basin.  Computer models are getting better at predicting these periods of increased likelihood of development. The current models are predicting that drier, sinking air is now moving into the Atlantic Basin.

Figure 1: Sinking Air (red-brown) and Rising Air (green) Through 8/14

Figure 1 is from the climate forecast system website (http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml).  It depicts areas of sinking air (reddish-brown) and rising air (green) in 5 day intervals starting on July 25th.  Note the deep reddish-brown area of sinking air forecast to dominate much of the Atlantic Basin over the next week.  The sinking air moves out after about the first week of August and is replaced by the green color of rising air by the 9th of August.  More rising air means increased thunderstorms across the Atlantic Basin, and an increasing chance of tropical development.

Figure 2, below, from the Santa Barbara, CA Research Group (http://www.icess.ucsb.edu/asr/mjo_forecasts.htm) represents another forecast for the next few weeks. This one predicts what’s called “Outgoing Long-wave Radiation” or “OLR” for short.  It’s a little complex to explain fully here, but OLR is greatest when thunderstorm activity is less across the tropics.  More thunderstorms, on the other hand, means decreased OLR.  The blue areas in Figure 2 represent decreased OLR, meaning increasing thunderstorms.  The reverse is true for the areas of greens and yellow.

Figure 2: Outgoing Long-wave Radiation

Figure 2 is also indicating that rising air, meaning increased thunderstorms, moves into the Gulf of Mexico and the Caribbean Sea after about the 4th of August, peaking the second and third week of August.  While a prediction of increased thunderstorm activity alone doesn’t mean an increased chance of tropical development, wind shear is also forecast to diminish over the next few weeks.  The combination of lower wind shear and increased thunderstorm activity is pointing toward a burst of tropical cyclone development starting around the 10th of August.

This will likely be the real start to the 2010 hurricane season. After about August 10th, we may experience very few days without at least one active named storm in the Atlantic Basin through about mid October.   Use the next 5-10 days to complete any remaining hurricane preparations, as I don’t think we’ll be seeing such a prolonged break in activity until mid October.

 Comment on this post

 Print this post

You can leave a response, or trackback from your own site.