Tag Archives: Subtropical Storm Alex

Subtropical Storm Alex Develops over East Atlantic

A low pressure system over the eastern Atlantic Ocean has been classified as Subtropical Storm Alex by the National Hurricane Center.  At 4:00 p.m. EST on Wednesday the center of Subtropical Storm Alex was located at latitude 27.1°N and longitude 30.8°W which put it about 785 miles (1260 km) south-southwest of the Azores.  Alex was moving toward the northeast at 14 m.p.h. (23 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 990 mb.

Subtropical Storm Alex evolved out of an extratropical cyclone that formed off the southeastern coast of the U.S. late last week.  The extratropical cyclone cycled through the typical stages exhibited by low pressure systems in the middle latitudes as it moved eastward across the central Atlantic Ocean.  It eventually became an occluded extratropical cyclone over that region.  The low pressure system moved south on Tuesday, which placed it over slightly warmer Sea Surface Temperatures (SSTs).  As it began to extract more energy from the warmer ocean, the fronts attached to the low pressure system began to dissipate.  The low began to take on a more circular shape and convection began to intensify around the center of circulation.  A more circular shape with no fronts and taller clouds prompted the National Hurricane Center to classify the low as a subtropical storm.

A subtropical storm is a hybrid low with some characteristics of a tropical cyclone (circular shape and no fronts) and some characteristics of an extratropical cyclone (cooler air aloft).  Subtropical Storm Alex has a well organized low level circulation.  There is a clear area in the center that looks a little like the eye of a hurricane.  The center is surrounded by a ring of taller clouds.  Spirals bands of clouds are rotating around the core of the circulation.  However, the vertical structure is different from a tropical cyclone.  Subtropical Storm Alex is under an upper level trough and the upper level divergence is limited.  Also, the clouds in Alex are not growing as tall as the clouds in a tropical cyclone.

The environment around Subtropical Storm Alex would normally be considered to be unfavorable for intensification of a tropical cyclone.  The SSTs are near 23.5°C.  However, since Alex is near the center of an upper level trough, there is not much vertical wind shear.  So, there could be a chance for some intensification during the next 24 hours.  Subtropical Storm Alex will move over cooler SSTs and it is likely to make a transition back to an extratropical cyclone in two or three days.

The upper level trough is steering Alex toward the northeast and a general northward motion is expected to continue for the next several days.  On its anticipated track Subtropical Storm Alex could approach the Azores in about 36 hours.  It could bring strong winds and locally heavy rain when it moves over the Azores.

Subtropical Storm Alex is the first tropical or subtropical cyclone to form over the North Atlantic Ocean in January since 1978.  It is only the fourth tropical or subtropical cyclone on record to form over the Atlantic Ocean in January since 1851.