1:25 PM | *Tropical Storm Dorian approaching the Windward Islands…could reach hurricane status in the near term over the eastern Caribbean, but will battle with dry air*
Paul Dorian
The latest GOES-East “Geocolor” satellite image shows the two areas of interest with Tropical Storm Dorian (lower, right) and an elongated area of clouds over the western Atlantic (upper, left). Courtesy NOAA/NESDIS/STAR
Overview
After a quiet start to the month in terms of Atlantic Basin tropical activity, the last week of August is beginning with one tropical system over the western Atlantic Ocean and a tropical storm nearing the Caribbean Sea. Tropical Storm Dorian is fast approaching the Windward Islands and it could become a hurricane once over the warm waters of the eastern Caribbean. There is currently some dry air over the Caribbean Sea out ahead of Tropical Storm Dorian which could limit its intensification prospects later in the week and its ultimate track will be quite crucial. A track over the rugged terrain of Hispaniola Island, for example, would likely weaken the system, but that is not a certainty at this point. Finally, the eventual path and intensification of the initial tropical system over the western Atlantic could, in turn, have an impact on TS Dorian depending on its movement and development in coming days.
The “total precipitable water” loop indicated high moisture content (orange, red) associated with Tropical Storm Dorian near the Windward Islands and over the western Atlantic associated with the initial tropical wave. There is, however, drier air over the Caribbean (green, blue) and this could have an impact on intensification prospects for TS Dorian in coming days. Courtesy CIMSS/University of Wisconsin/NOAA
Discussion
Over the weekend, one tropical wave pushed westward from the Bahamas to over the Florida Peninsula – limiting its development chances for about 24 hours – while a second system intensified into a tropical storm over the central tropical Atlantic. The initial wave has since pushed to the northeast and is now back over warm waters of the western Atlantic and it may slowly intensify in coming days. Meanwhile, Tropical Storm Dorian is now moving 14 mph to the west with 60 mph maximum sustained winds and is closing in on the Windward Islands. There is a chance Dorian reaches hurricane status over the next day or two as it pushes over the eastern Caribbean Sea where sea surface temperatures are quite warm for this time of year.
This map shows a series of forecast tracks by numerous computer forecast models for Tropical Storm Dorian with the official NOAA/NHC path in red (circles as markers). Courtesy NOAA, sfwmd.gov
There is some dry air positioned over the Caribbean Sea that has actually pushed westward by trade winds in recent days from the African continent and it can inhibit intensification later in the week. In addition, the likely track of TS Dorian will bring it awfully close to Puerto Rico and then the Island of Hispaniola (Dominican Republic/Haiti). A trek over Hispaniola usually weakens a tropical system as there is quite a bit of rugged terrain (highest elevation over 10K feet) and the wind shear tends to disrupt the inner circulation field of a tropical system. The exact path is just too early to define, yet it’ll be quite crucial. Once by these two Caribbean islands (i.e., Puerto Rico, Hispaniola), whatever remains of TS Dorian could very well re-strengthen as it heads towards the Bahamas and then Florida - those areas could be impacted during the upcoming Labor Day weekend.
Tropical Storm Barry churned slowly over the northern Gulf of Mexico during mid-July and had an impact on sea surface temperatures through the upwelling process. The tropical system now over the western Atlantic will be monitored to see if it too can have an impact on sea surface temperatures underneath which could, in turn, have an influence on TS Dorian should it follow a similar path. Courtesy NOAA
A complicating factor is the tropical system over the Western Atlantic. If this system intensifies over the next couple of days, it could actually have an impact on sea surface temperatures underneath through a process called upwelling which, in turn, have an impact on TS Dorian should it follow a similar path. [Upwelling results in colder water underneath the surface to rise up and this could quickly change temperatures from above-to-below normal in a given region]. Tropical Storm Barry pushed northward through the Gulf of Mexico in mid-July and briefly attained hurricane status as it made landfall in southern Louisiana. Its slow churn over the Gulf of Mexico resulted in a noticeable drop in sea surface temperatures after its passage which inhibited subsequent tropical storm activity for many days.
Stay tuned…plenty of questions still have to be ironed out.
Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com
Video discussion: