STARDATE 220917   2300  EDT  


Here is the Saturday evening update and model discussion regarding the future of Tropical Storm Fiona. The system continues to look like a classic sheared moderate sized Tropical Storm. The evening satellite picture does look a little better compared to Saturday morning but there is still l quite a bit of shear and it is going to have significant interactions with the big island of Hispaniola during the next two days. The last couple of advisories from the NHC are taking Fiona to minimal hurricane intensity in the next 2 days but I remain skeptical about this. There is no doubt that once Fiona clears the big islands in the Caribbean and turns due north into the open waters of the west Atlantic Ocean, it will likely intensify significantly. But I am not convinced Fiona is going to make hurricane intensity during the next two days. I could be wrong but right now I am just not convinced.




In the last update WxRisk did which was a video update over on the YouTube channel, we talked about the possibility that because Fiona would stay rather weak, it would track south of the big Island’s or ride along the northern coast of Hispaniola and far eastern Cuba. This would allow for a delayed turn to the NW and curve into the Bahamas and pose a threat to Florida and the southeastern states.  WxRisk did not  think that was a high probability event but it was a potentially viable scenario nonetheless.


That scenario is pretty much off the table based upon the data of the last 24 hours. If you compare the actual track of Fiona to the forecast positions in the last 36 hours, you will see that the system has been consistently to the south of the official forecast and the models. Not by much but it is clearly running a little south of the forecast tracks in the forecast models. All things being the same this kind of minor deviation can lead to significant changes down the road but in this particular case that is not going to matter because the Trough in the jet stream coming off the East coast and Mid-Atlantic region at 66 hours appears to be a bit stronger on all the model data on this Saturday evening.


 This first image shows the 500mb map valid for Sunday night across North America and the coastal waters. The most important thing to notice here with Fiona is the Ridge in the southwest Atlantic north of the system, which WxRisk has highlighted in purple so you can see its shape and position. In North America there are two large and powerful upper LOWs in the jet stream:  along the central California coast bringing significant rain and wind to much of the Pacific northwest and south of Greenland. There is a large DOME (enhanced Ridge) located across Texas and Oklahoma bringing record heat to that area. And there was a weak Trough in the jet stream moving through Minnesota and Wisconsin.

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 At 66 hours this Midwest Trough in the jet stream amplifies significantly as it moves into the Middle Atlantic and New England. This begins to attack the Western flank of the Ridge in the southwest Atlantic north of Fiona. With the western flank of the Ridge weakening, Fiona begins to turn more sharply to the north.

  click on the images  to see full size


By 102 hours or Wednesday afternoon September 21, the entire Western flank of the ridge in the jet stream across the Southwest Atlantic has completely disappeared (again highlighted in purple). The first Trough is now located in the Canadian Maritime Provinces but a much stronger Trough with a significant and surface cold front for the middle of September is driving into the Great lakes and headed for the Ohio Valley, the Mid-Atlantic, and New England by September 22nd.

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This Trough is going to amplify as it swings into the East Coast so that by September 20th /144 hours  it will become a massive Trough stretching from Labrador Canada to Georgia and the Carolinas. This Trough will drive a significant cold front through the entire eastern half of the country with rain and thunderstorms followed by a real autumn blast of chilly air with gusty north winds. There is a real good chance that the massive East Coast Trough is likely to capture hurricane FIONA and pull it due north into New Brunswick Canada and the Canadian Maritime Provinces Late on September 23rd into September 24.

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It is a bit early to know this for certain, but it is possible for Hurricane Fiona could be a storm of exceptional intensity and ferocity for the Canadian Maritime Provinces. Much will depend on how the Fiona interacts with the massive 500mb Trough along the East Coast on September 23rd. The operational European model shows an extremely dangerous and well quite frankly historic scenario for the Canadian Maritime Provinces because the East Coast Trough captures Fiona and pulls it into the Canadian Maritimes with a forward speed over 50 mph !  But it is also possible that the Trough may act as a “kicker” and drive Fiona further away from the coast. The operation of European scenario needs to be watched carefully here.

         click on the images  to see full size


Finally, as WxRisk has been talking about for the past several days, there is as a massive Trough in the jet stream which is going to develop across the entire eastern half of the country during the last two days of September. This massive Trough will bring a significant cold air outbreak of autumn air.  The amplification of this pattern across North America will occur because of the massive typhoon headed for Japan right now Those of you looking for the first rule surge of chilly air of the season better get ready — if the model data is correct this cold front and the cold air behind it is going to knock you on your ass.

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