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Unnamed subtropical storm in the 2013 Atlantic hurricane season


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An unnamed subtropical storm appears to have developed just after the official end of the Atlantic hurricane season. Post-season analysis from NOAA indicates that this subtropical storm developed on the 5th of December just to the south of the 

Azores. The system didn't live for very long, though, as it lasted only for 2 days.

 

Pre-designation synoptics

 

The system could first be recognized on the 29th of November. This can be seen in the GFS chart below:

Posted Image

GFS 29 November pressure analysis

 

The precursor of the unnamed subtropical storm can be seen as the sub-1010 hPa trough (at the surface) at the extreme southwestern part of the map. Note that there is also a weak 500 hPa trough associated with the low (as indicated by the lighter orange colors surrounded by darker orange colors).

 

On the second of December, the low has deepened somewhat:

Posted Image

GFS 2 December pressure analysis

 

The precursor low pressure area can now be seen just to the south of the Azores as a sub-1005 hPa low. Note that the 500 hPa trough associated with the surface low has attained a connection with the parent trough far to the north of the system.

 

At the 4th of December, the low has attained subtropical cyclone status. Moreover, the system has attained its minimum surface level pressure by then:

Posted Image

GFS 4 december pressure analysis

 

The storm has reached a pressure of less than 1000 mb in this chart. The 500 hPa trough has once again become disconnected from the parent trough to its north, and therefore, it can be considered a cut-off low.

 

Consequences for the 2013 Atlantic hurricane season

 

As a result, the total storm count has been upped to 14, indicating a slightly above-median activity in this basin. However, as mentioned previously on other parts of this forum, the hurricane and major hurricane count were well below normal, with only two storms attaining hurricane intensity and none of them reaching major hurricane intensity.

 

It is interesting to note, though, that even in the Satellite era, storms can still go unnoticed by experts as well.

 

The full synoptic history and meteorological background can be found in the link below:

 

http://www.nhc.noaa.gov/data/tcr/AL152013_Unnamed.pdf

 

Sources:

http://www.nhc.noaa.gov/data/tcr/AL152013_Unnamed.pdf

http://www.wetterzentrale.de/topkarten/fsavneur.html

Edited by Vorticity0123
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The National Hurricane Center (NHC) announced last week that the hurricane season of 2013 had one more storm that should have been named--a short-lived low that developed south of the Azores during early December, which became a subtropical storm on December 5. "Should-Have-Been-Named-Subtropical-Storm-Nestor" reached top sustained winds of 45 mph. The storm formed over unusually cool waters of 22°C (72°F), and brought sustained 10-minute winds of 37 mph with a gust to 54 mph near 00 UTC December 7 to Santa Maria in the southeastern Azores. With this addition, the 2013 Atlantic season ended with 14 tropical and subtropical storms. Two, Ingrid and Humberto, became hurricanes, but neither became a major hurricane.

 

http://www.wunderground.com/blog/JeffMasters/show.html

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