Tropical Outlook Graphic for September 19, 2021 showing Tropical Storm Peter, Tropical Storm Rose, the Remnants of Odette to the north and what will become Tropical Storm Sam off the African Coast. National Hurricane Center Graphic.
Two Tropical Storms Present as Active Hurricane Season Shows No Sign of Slowing
Shortly after Tropical Storm Peter developed on September 18, Tropical Depression Seventeen formed out of a low pressure south of the Cabo Verde Islands. At the same time, forecasters watched another area of low pressure about to move off the Africa Coast into the same area where Depression Seventeen organized. By mid-afternoon on the nineteenth, Depression Seventeen further organized into Tropical Storm Rose, the seventeenth named storm of the 2021 Atlantic Hurricane Season.
In their initial advisory, the NHC forecast provided a nearly straight track to the northwest with Rose maintaining strength through Wednesday before weakening to a depression on Thursday and Friday. By Tuesday, the track changed to include a right turn to the northeast on Thursday as Rose transitioned to a post-tropical depression.
Increasing wind shear caused Tropical Storm Rose to weaken sooner than initially expected as its deep convection separated from the storm center. By 11 PM Atlantic Standard Time on Tuesday, Rose had 35 MPH sustained winds and the NHC downgraded Rose to a Tropical Depression. Forecasters expected further weakening as the environment became increasingly hostile. The tropical storm began a transition to a post-tropical cyclone that evening and had lost all tropical characteristics by Thursday morning. The National Hurricane Center issued the last advisory on Tropical Cyclone Rose.
Tropical Storm #Rose has formed in eastern tropical Atlantic - the 17th named storm of 2021 Atlantic #hurricane season to date. Only two other years in satellite era (1966 onwards) have had 17+ Atlantic named storms by September 19: 2005, 2020. pic.twitter.com/AVvvgdap9s— Philip Klotzbach (@philklotzbach) September 19, 2021
Tropical Storm Sam on September 23, 2021. To the right is the African Coast with another tropical wave about to move over the same waters that produced Tropical Storm Sam. Sam is forecast to become a Major Hurricane next week.
NOAA Satellite Image
Tropical Storm Sam to Become a Major Hurricane
Shortly after Tropical Depression Seventeen formed south of the Cape Verde Islands, another system was moving off the coast with a good chance for formation into a tropical depression. Depression Eighteen formed in the same region as Tropical Storm Rose and strengthened to Tropical Storm Sam on Wednesday, September23.
The current forecast for Sam has it strengthening to a Hurricane on Friday and a Major Hurricane late Saturday or early Sunday. The forecast track indicates Sam will continue on an east-northeast track through Saturday with a gradual turn to the northeast by Sunday.
Although Sam’s exact beyond Saturday is unknown, it will probably turn north of the Leeward Islands. This storm could follow a track that brings it to the East Coast, The Bahamas, or Bermuda. However, a small chance exists that it could come close to the Leeward Islands and Puerto Rico.
Those living in the Leeward Islands, Puerto Rico, the Bahamas, Bermuda, and the East Coast, including Florida, should continue to monitor Sam and begin their preparations for a hurricane.
Tropical Storm Sam is the second earliest Eighteenth Named Storm on Record, surpassing the 2005 season and second only to Hurricane Sally which formed on September 11, 2020 and made landfall at Gulf Shores, Louisiana.
Like Rose, Depression Peter has lost all tropical characteristics. The post-tropical cyclone remnants have dissipated, and the NHC issued its final advisory on Wednesday.
The remnants of Tropical Cyclone Odette continue to produce gale-force winds over the north-central Atlantic. Tomorrow, the low-pressure system should move south over somewhat warmer waters and could organize to a subtropical or tropical cyclone on Friday or Saturday. The NHC gives the low-pressure system a 60 percent of reorganization over the next five days. Regardless, over the weekend, wind shear will limit development or cause the system to lose any tropical characteristics that it acquires.
Another Tropical Wave is moving off the West Coast of Africa over the weekend into the same region that produced Tropical Storm Sam. Conditions in this region are expected to remain conducive to development and could form a Tropical Depression next week. The next name on the list of storms for 2021 is Teresa.
Only three names remain for the 2021 Hurricane Season before it ends November 30. If the last name is used, the NHC will assign names from the new alternative list created following the record setting 2020 Hurricane Season.
Tropical Storm #Sam has formed in the eastern tropical Atlantic - the 18th named storm of the 2021 Atlantic #hurricane season to date. Only 1 season on record has had 18+ Atlantic named storms by 23 September: 2020. 2020 had 23 named storms by 23 September. pic.twitter.com/AGFg37ljxw— Philip Klotzbach (@philklotzbach) September 23, 2021
BREAKING: Tropical Storm #Sam has formed over the open Atlantic. Sam is about 1,745 miles east-southeast of the northern Leeward Islands and is expected to strengthen into a major hurricane in the coming days: https://t.co/nJhls3lFdw pic.twitter.com/kDhfLdB9RO— Breaking Weather by AccuWeather (@breakingweather) September 23, 2021
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