21 September 2015

Ida strengthens in central Atlantic

Since my last update on Wednesday the 16th, Tropical Depression 9 dissipated on Saturday.  The wave behind it was upgraded to Tropical Depression 10 on Friday morning, and later upgraded to Tropical Storm Ida on Friday night.  Ida is the season's ninth named storm.  Using 1981-2010 as the climatology, the ninth named storm forms on September 29 during an average season.

Ida has not done much though, as it turned to the northwest and encountered strong vertical shear. However, environmental conditions have been improving and Ida has strengthened as a result.  As of Monday morning, peak winds are estimated at 50mph.  It is forecast to remain nearly stationary but also to gradually intensify over the next five days. While it does stand a chance of becoming the season's third hurricane, it is not a threat to land.

Elsewhere, no new formation is expected this week.  But global models are in agreement on something brewing in the southern Gulf of Mexico this weekend, and generally tracking it northward.  This is absolutely not a cause for concern, it is just something to monitor in the models for now... the disturbance doesn't even exist yet.  Below is output from three global models (ECMWF, GFS, and CMC), all valid on Sunday evening.  The colored field is the 850mb vorticity, which is a measure of the curvature of the low-level wind.

850mb vorticity from the 00Z runs today, valid in seven days.  ECMWF is on the left, GFS is in the middle, and CMC is on the right. (tropicaltidbits.com)

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