(PM)- Tropical Storm Dorian is expected to strengthen into a hurricane late this week before threatening the east coast. The storm currently sustains 60mph winds moving NW at 13mph and likely to threaten Puerto Rico tomorrow before exiting the Caribbeans.
Tropical Storm Dorian was expected to travel further west over the open waters of the Caribbean under more harsh conditions. This would’ve been fine for a weaker storm as there is dry air as well as stronger wind shear. Not to mention a track into the Dominican Republic is a death sentence for many tropical cyclones. The tall mountains of the Dominican tend to disrupt the inner core of storms.
However, over the last few days models shifted further north and east moving the storm away from the Dominican and closer to Puerto Rico. This makes it much more likely that the storm would survive into the open waters north of the Caribbean and eventually into the Bahamas.
This spells trouble for the United States as there is a building ridge near Bermuda guiding the storm west.
Currently Dorian is looking like a much healthier system this morning but is still fighting off some dry air. Convection is firing around the center but is having a hard time staying sustained. The storm has become more symmetric which is a sign of strengthening. However, I think we see most of our strengthening after the storm moves into open waters past Puerto Rico.
The current forecast nearly goes along with my thoughts with a landfall in north eastern Puerto Rico. I believe it is becoming more likely that landfall in Puerto Rico does not occur and just misses to the east as that has been the trend.
Above is the ECMWF model 500mb height anomalies. The model is showing a building ridge indicated by the yellows and oranges to the north of the system. This makes an escape out to sea hard as the ridge will likely push the storm west. The ECMWF does have a bias to over amplify ridges, that is mostly evident come winter but it is something to keep in mind.
The GFS or American model shows Dorian in nearly the exact same position albeit with a weaker and further east placed ridge. If this ridge breaks down faster there is still a pathway for Dorian to escape without making direct landfall. However, the GFS is also know for breaking down ridges too fast but the model did get a massive upgrade just a few months ago.
The exact track will be mostly determined by the strength of that ridge. The picture will be more clear in the coming days. A stronger ridge will send the storm into Florida and possibly into the Gulf of Mexico before likely turning north and east being picked up by an incoming trough. A weaker ridge may still push Dorian west but give an escape route if the trough can swing in fast.
The storm looks to be headed into a favorable environment for strengthening as we take a look at current sea surface temperatures.
Sea surface temperatures are ranging from 28-30 degrees Celsius which is supportive for a strong hurricane in the Bahamas and possibly within close proximity to the United States.
Above is a very useful but not perfect graphic. It uses sea surface temperatures as well as a combination of a few other factors to determine the potential minimum pressure and maximum wind speed for a tropical cyclone. In the region where Dorian will be entering, the estimated minimum pressure and wind speed support a strong hurricane.
However those maps cannot be taken as a forecast as they do not take other factors into account.
Dorian is doing a good job of fighting off dry air unlike yesterday where there was dry air sneaking into the center. If the storm took a track further west as initially thought Dorian would have run into much less favorable mid-level dry air however that is not the case. In the Bahamas the air is also very moist and will likely not be an inhibiting factor.
The outflow seen around the core of the storm looks very healthy. It looks as if a period of strengthening is likely to occur, especially once further north.
Dorian is being affected by wind shear on the northeastern side of the storm, however, I mentioned before that outflow still looks good. It seems as though the storm is not being too affected by the strong mid level shear in the atmosphere. Dorian is headed into a high shear environment tomorrow but will exit it fast. This may put a cap on the strengthening for the next 48 hours. Shear in the Bahamas and off the Florida coast looks to relax a bit which is a bad sign.
Overall, the environment Dorian is headed into looks conductive for a strong hurricane with rapid intensification possible. I like the NHC forecast pinning this at a category 2 hurricane just before landfall but I can certainly see that rising.
The Spaghetti models mostly concentrate on a category 2/3 storm with a cluster at a category 1. The NHC tales a middle of the road approach at a weak category 2.
Timing for this system currently looks similar across the board and most models. The GFS has a hurricane making landfall in northern Florida early Monday morning. The ECMWF is a bit faster late Sunday night.
If there is a landfall which is still a big if, it looks to occur sometime next Sunday into Monday. Remember, this is still a 5 day forecast and those are relatively volatile in exact track and intensity.
Overall, from Miami to the Carolina’s need to be on watch and start planning for a potentially strong hurricane landfall. Updates will be provided as they come out. – Michael Barletta