06 September 2015

Fred and Grace spinning in far eastern Atlantic

On Saturday afternoon, Fred was downgraded to a Depression, again.  As of Sunday morning, it remains a Depression, but is forecast to regain tropical storm status by Tuesday as it moves toward a more favorable environment.

It has been a tropical cyclone for almost 8 days, and apparently, the normal environmental thresholds for TC maintenance don't apply to Fred, so it could be around for quite a while longer!  It has begun recurving to the north, and is forecast to head toward the northeast over the next 5 days.

As I hinted at in Friday's update, Grace is indeed now an active storm.  An easterly wave that left the African coast on Thursday became Tropical Depression 7 on Saturday morning, and then was quickly upgraded to Tropical Storm Grace on Saturday afternoon.  Grace is the 7th named storm of the 2015 season, and climatologically, the 7th named storm forms on September 12.  However, in terms of ACE (Accumulated Cyclone Energy), the season is still only at about 55% of average for this date.

Large-scale visible satellite image of Grace from 9:15am EDT today.  The Cape Verde islands are to its northeast. The milky color to the west and north of the storm is indicative of dusty, dry, stable air from the Sahara. (NRLMRY)
Grace is on a strengthening trend, and is tracking west at 13 mph.  For reference, it is located about 1200 miles southeast of Fred.  Models generally agree that it will reach the Leeward Islands region in about 6 days (Saturday-ish).  Here I show a selection of global and regional dynamical model 5-day forecast tracks, as well as the NHC forecast (OFCI).

However, it will be slamming into a wall of strong vertical wind shear on Wednesday, which should quickly put an end to any intensification that may occur in the meantime.  Models are currently in unanimous agreement on this.  The map below shows the forecast wind shear valid late Wednesday night.... Grace is the 1008mb Low that you see just east of the Lesser Antilles, nestled right up into the subtropical jet.  Typically, wind shear over 20kts is detrimental to tropical cyclones, so the 40kt+ swath cutting through the tropics would certainly have an impact on it.

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