20 September 2021

Watching far eastern Atlantic for next storm... Sam?

Since my previous post on Friday, we have had Odette, Peter, and Rose form in the Atlantic!  And, we're likely going to see the season's 18th named storm form this week: Sam.

Odette (15L) was a named storm for only a day, and came from the area of interest that was off the North Carolina coast on Friday.  The other two areas that were highlighted in that post became Peter (16L) and Rose (17L), and they are both still active. 

Neither Peter nor Rose will be able to strengthen much, and both will remain far out in the ocean.  Both are facing wind shear and dry air to different degrees.

Peter is located just north of the Leeward Islands and is close to a strong upper-level low pressure system which is forcing the thunderstorm activity east of the circulation center.  Rose is west of Cabo Verde and is close to ingesting lots of dry Saharan air.  Both are forecast to track toward the northwest then north in the coming days.  The only potential concern would be Bermuda this weekend, but impacts from Peter would not be significant.

It's worth pointing out that Rose became the season's 17th named storm on September 19th.  Since 1851, only two other seasons had the 17th named storm so early in the year: 2005 and 2020.  Rose is also still a name from the original 1979 list and has never been used before now! 

Now on to what will almost certainly become Sam: Invest 98L.  This easterly wave left the west coast of Africa on Sunday morning and has been strongly favored by the model guidance to develop and to maintain a track in the deep tropics for a while.

The model guidance is generally bullish on this system, eventually.  It's in a tight spot right now, with Rose immediately to its northwest and Saharan air streaming off the continent to the north. 

The latest deterministic (single higher-resolution run compared to the ensembles) European model run brings this storm very close to or over the northern Leeward Islands next Wednesday as a hurricane.  The latest American model run is two days slower and 275 miles farther north.  Clearly, there is some disagreement to sort out in the coming days, but they both have a hurricane tracking through the deep tropics next week.

European (top) and American (bottom) deterministic runs, both valid when the storm is at the longitude of the Leeward Islands.  For the European run, that's next Wednesday, but next Friday for the American model.

Looking at the updated ACE (Accumulated Cyclone Energy) chart, 2021 is now at about 117% of average for the date.  This time of year, it takes a decent amount of activity just to keep up with climatology, and a couple of low-end tropical storms don't quite cut it, so we're creeping closer to average every day... for now.

1 comment:

  1. Thanks, Brian!
    Curious about the discrepancy between Sam’s European model and the U.S.