16 September 2016

Atlantic now has three named storms for first time in four years

Ian, Julia, and Karl are all tropical storms now, a level of activity not seen in the Atlantic since 2012 when Isaac, Kirk, and Leslie were all active. However, it will be hard to touch the record of four simultaneous hurricanes in the Atlantic: Georges, Ivan, Jeanne, and Karl in 1998 (note that Georges, Ivan, and Jeanne have since been retired).

Infrared satellite image of the Atlantic basin on Friday morning. (CIMSS)
Contrary to model guidance, nature decided that Julia was not finished yet, and it was re-upgraded to a tropical storm on Thursday afternoon.  The official forecast still calls for it to weaken and remain nearly stationary though, so it is not expected to become a threat to land.

Ian is still clinging onto tropical cyclone status, though barely.  This is the last you'll hear about it, but it did hang around long enough to assist with the "three simultaneous named storms" statistic!

And last but not least, Tropical Depression 12 was upgraded to Tropical Storm Karl, the 11th named storm of the season.  In an average season, the 11th named storm forms on October 28!  But as before, the overall activity as measured by ACE (Accumulated Cyclone Energy) is still lagging behind... roughly 74% of average for this date.  In other words, the season has had a lot of weak storms: they get named but don't get very strong or last for very long.

Karl is expected to remain relatively weak for the next several days, but by the middle of next week it could be in a position to intensify as it heads west. This graphic below shows a three-day forecast of the surface pressure and mid-level humidity -- Karl is the low pressure near 47°W surrounded by dry air (the next easterly wave behind it may also get named next week... it would be Lisa).

 In the longer range, most models still agree that it will get stronger and track toward the west-northwest.  It's too early to say if it will recurve toward Bermuda or keep a heading more toward the U.S.  Shown here is a plot of track forecasts from the GFS ensemble (a global dynamical model run multiple times with slightly different initial conditions to simulate uncertainty).  The lines are colored by intensity.  At this point, the majority have it recurving before it reaches 70°W, but that can change.

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