Jul 24, 2013

Tropical Storm Dorian

The 4th named tropical cyclone of the season has formed over the far Eastern Atlantic this morning, its named Dorian.  It is moving rather briskly on west and slightly north track at 22 mph and was located about 310 to the SSW of the westernmost Cape Verde, Islands. Here is the latest IR satellite image.
IR Satellite picture from 945AM EDT 24 July of Africa with T.S. Dorian on the lower left 

As you can see from the satellite photo Dorian is a relatively small cyclone. Currently it is in an environment of low shear [ wind  speeds aloft < 20kts] and warm sea-surface temperatures [SSTs] of greater than or equal to 26°C, both favorable for some development. However once it moves west of approximately 35° W longitude environmental conditions will become less favorable as dry Saharan air will be close to the storm's circulation:




and wind shear will also be increasing: 


The above map shows the forecast track of Dorian along with the expected wind shear along it. Over the short term ( i.e., the next 24-36 hours) Dorian is expected to strengthen slightly with winds increasing to near 50 knots; then it is expected to weaken to a "minimal" tropical storm with winds staying near 40 knots as it moves over slightly cooler SSTs and eventually increasing westerly wind shear. However once it passes by the cooler water, SSTs warm to 26°C or greater (west of 43°W), thus the warmer waters below "may" offset the increasing share above, thus the call for Dorian to maintain tropical storm strength over the next 5 days.

Keep in mind that small tropical cyclones (the radii of Dorian's tropical storm force winds [34 kts/40 mph] extends only 40 nautical miles to the NE and 30 nautical miles to the SE of the center) can rapidly weaken, especially in less than favorable environmental conditions BUT they can also "survive" and hold there own, too because the small size can actually "allow" it to "avoid" these poor conditions.


Here is the current forecast track from the NHC for Dorian based on the 24 July 2013 11 AM EDT data: