Good evening from Southern Connecticut Weather.
On July 28, I first posted about a tropical wave in the central Atlantic that was worth watching as it had the potential to develop in the Bahamas. In that post, I said that one of the reasons to watch with a casual eye at the time was the steering pattern not immediately reflecting an easy and harmless recurve. Fast forward to today, and we have hurricane warnings along the west coast of Florida and tropical storm warnings for parts of the southeast coastline as Tropical Storm Debby--in the Gulf not Bahamas--gradually organizes and should become a hurricane by the time it makes landfall in the next 24 hours.
For Connecticut, a series of features make it increasingly likely, but far from certain, that we see some kind of influence from Debby during the next week. Much of this discussion will focus on how that could occur. Before going any further however, let's level set.
This is not something to panic about or jump to conclusions over, which is easy to do whenever anyone hears about a tropical system. We are still quite a distance away from any indirect impacts let alone direct impacts. As always, we preach preparation over panic, and this discussion is intended to give you a first look at what will be an evolving forecast for Debby or its remnants impacting our weather.
With that out of the way, let's dive in.
On July 28, I first posted about a tropical wave in the central Atlantic that was worth watching as it had the potential to develop in the Bahamas. In that post, I said that one of the reasons to watch with a casual eye at the time was the steering pattern not immediately reflecting an easy and harmless recurve. Fast forward to today, and we have hurricane warnings along the west coast of Florida and tropical storm warnings for parts of the southeast coastline as Tropical Storm Debby--in the Gulf not Bahamas--gradually organizes and should become a hurricane by the time it makes landfall in the next 24 hours.
For Connecticut, a series of features make it increasingly likely, but far from certain, that we see some kind of influence from Debby during the next week. Much of this discussion will focus on how that could occur. Before going any further however, let's level set.
This is not something to panic about or jump to conclusions over, which is easy to do whenever anyone hears about a tropical system. We are still quite a distance away from any indirect impacts let alone direct impacts. As always, we preach preparation over panic, and this discussion is intended to give you a first look at what will be an evolving forecast for Debby or its remnants impacting our weather.
With that out of the way, let's dive in.
Above: the latest Weather Prediction Center (WPC) rainfall forecast for the continental U.S. for the next seven days. Obviously we are focused on the east coast. You can see that from Florida to New England the WPC believes the next week will be quite wet. Most (but not all) of this rainfall is predicated on the track and influence of Debby and/or its post tropical remnants. This gives you a sense of the reasonable rainfall potential over the coming week.
Monday
Before we start the potential deluge, we need to deal with tomorrow's heat and storms. Hazy, hot, and humid, even down to much of the coastline. Tomorrow will bring us the last sun we could see for a while, and it'll come with more hot and humid conditions. Highs will be in the upper 80s to low 90s for most, and the humidity will bring heat indices well into the 90s again. By afternoon, we're looking at another chance of strong to severe thunderstorms, especially in northern and western CT. Wind and hail are the greatest hazards, much like the last few days. Storms don't look as widespread as today, but it's worth staying weather aware.
Monday is when what should then be Hurricane Debby makes landfall along the west coast of Florida. The track is likely to slow substantially, so Debby will be tied up over the area through the day with no influence on our weather.
Monday
Before we start the potential deluge, we need to deal with tomorrow's heat and storms. Hazy, hot, and humid, even down to much of the coastline. Tomorrow will bring us the last sun we could see for a while, and it'll come with more hot and humid conditions. Highs will be in the upper 80s to low 90s for most, and the humidity will bring heat indices well into the 90s again. By afternoon, we're looking at another chance of strong to severe thunderstorms, especially in northern and western CT. Wind and hail are the greatest hazards, much like the last few days. Storms don't look as widespread as today, but it's worth staying weather aware.
Monday is when what should then be Hurricane Debby makes landfall along the west coast of Florida. The track is likely to slow substantially, so Debby will be tied up over the area through the day with no influence on our weather.
Above: the SPC outlook showing a slight risk for part of northern and NW CT tomorrow.
Tuesday-Wednesday
Perhaps there is some influence from the greater flow of Debbie, which will still be well to our south at this time, but overall we will have a trough move into the region from the north. That means we will see a front that brings relief from high temperatures, but that front slows significantly near the area. As that happens we will get southerly flow push moisture into the region, leading to our first potential period of moderate to heavy rain. It will not rain all the time, but both days should feature rain that may be heavy at times depending on the placement of the front, and either or both days could pose a flash flood risk.
The GFS and Euro wildly diverge on the track of Debby, but they are more or less in agreement on this trough/front bringing rain. After the GFS led the way with regard to handling Debby pre-development, now it looks like the Euro has pushed ahead in more accurately projecting the system. At least for now. As a result, I weigh the Euro/EPS a bit more than the GFS/GEFS here.
Perhaps there is some influence from the greater flow of Debbie, which will still be well to our south at this time, but overall we will have a trough move into the region from the north. That means we will see a front that brings relief from high temperatures, but that front slows significantly near the area. As that happens we will get southerly flow push moisture into the region, leading to our first potential period of moderate to heavy rain. It will not rain all the time, but both days should feature rain that may be heavy at times depending on the placement of the front, and either or both days could pose a flash flood risk.
The GFS and Euro wildly diverge on the track of Debby, but they are more or less in agreement on this trough/front bringing rain. After the GFS led the way with regard to handling Debby pre-development, now it looks like the Euro has pushed ahead in more accurately projecting the system. At least for now. As a result, I weigh the Euro/EPS a bit more than the GFS/GEFS here.
The WPC places all of CT in a slight risk of excessive rainfall on Tuesday into early Wednesday. That may be extended through more of Wednesday if the Euro like depiction proves to be more accurate. While we deal with increasing rainfall, it looks as if coastal and even inland GA and SC will receive potentially historic amounts of rain, hence the relatively rare high risk down there.
Thursday
Although it will be cloudy with a chance of showers, Thursday currently looks like it will be a drier day with lower humidity as the front will have passed to our south. Hopefully we can get some sun this day. By this time, Debby will still likely be well to our south, but moving northward or northeast toward the region.
Although it will be cloudy with a chance of showers, Thursday currently looks like it will be a drier day with lower humidity as the front will have passed to our south. Hopefully we can get some sun this day. By this time, Debby will still likely be well to our south, but moving northward or northeast toward the region.
Friday-Sunday
If there are direct impacts from Debby, this is the time. As I mentioned earlier, the GFS/Euro and their ensembles vary wildly on what will happen with Debby. By direct impacts, I mean either rainfall that comes directly from a close approach, or an unlikely New England landfall as a tropical system.
The impacts could happen in two stages.
Friday--Predecessor Rain Event
Very simply put, sometimes tropical systems when moving northward interact with a "nearby" trough, and the interaction aloft allows for a localized to widespread area of extremely heavy precipitation to fall. This is called a Predecessor Rain Event, or PRE. PREs can happen a thousand miles away from the actual center of a low, and the tropical storm or hurricane no longer needs to be at peak strength to trigger this heavy rainfall, though they sometimes are.
Across guidance we have seen this signal for days, and it has bounced around New England in individual model runs depending on the track of Debby or its remnants. Some runs have been prolific, producing rainfall totals over 4+ in 24 hours. This is the second potential period where we could get heavy rain.
The split on the guidance, particularly between the GFS on one side and the other global models on the other, is fairly dramatic. The GFS/GEFS keeps Debby suppressed to the south for longer, making it much less likely that Debby influences our weather directly during this period.
The Euro/EPS on the other hand, does essentially the opposite. Over the course of the week, the European Ensembles depicts an average of more than a month's worth of rain across the region, while the GEFS is robust but lower.
If there are direct impacts from Debby, this is the time. As I mentioned earlier, the GFS/Euro and their ensembles vary wildly on what will happen with Debby. By direct impacts, I mean either rainfall that comes directly from a close approach, or an unlikely New England landfall as a tropical system.
The impacts could happen in two stages.
Friday--Predecessor Rain Event
Very simply put, sometimes tropical systems when moving northward interact with a "nearby" trough, and the interaction aloft allows for a localized to widespread area of extremely heavy precipitation to fall. This is called a Predecessor Rain Event, or PRE. PREs can happen a thousand miles away from the actual center of a low, and the tropical storm or hurricane no longer needs to be at peak strength to trigger this heavy rainfall, though they sometimes are.
Across guidance we have seen this signal for days, and it has bounced around New England in individual model runs depending on the track of Debby or its remnants. Some runs have been prolific, producing rainfall totals over 4+ in 24 hours. This is the second potential period where we could get heavy rain.
The split on the guidance, particularly between the GFS on one side and the other global models on the other, is fairly dramatic. The GFS/GEFS keeps Debby suppressed to the south for longer, making it much less likely that Debby influences our weather directly during this period.
The Euro/EPS on the other hand, does essentially the opposite. Over the course of the week, the European Ensembles depicts an average of more than a month's worth of rain across the region, while the GEFS is robust but lower.
Track matters a lot, and there's substantial uncertainty. While the GFS/GEFS seem far too suppressed and actually eventually gets a remnant low off the southeast coast and out to sea, the other guidance bring a much closer approach, and some guidance introduces a low (but nonzero) New England landfall risk from remnants or a trough enhanced tropical storm Debbie. The closer Debbie gets to us, the more rainfall we see from a PRE and then the system itself.
Saturday & Sunday--potential close approach
Friday would potentially bring the PRE rainfall while Debby could make its closest approach by Saturday or Sunday. This would be the third potential period of heavy rain. This is really far out in tropical tracking terms, so expect a lot to change over the next few days. Below you'll see the latest versions of the GFS and Euro. The GFS buries this in the southeast while the Euro brings it further north before skirting out to sea to our south at the last second.
First the GFS. Note how it gets hung up in the south. This is an outlier for now and discounted by the National Hurricane Center (NHC)
Saturday & Sunday--potential close approach
Friday would potentially bring the PRE rainfall while Debby could make its closest approach by Saturday or Sunday. This would be the third potential period of heavy rain. This is really far out in tropical tracking terms, so expect a lot to change over the next few days. Below you'll see the latest versions of the GFS and Euro. The GFS buries this in the southeast while the Euro brings it further north before skirting out to sea to our south at the last second.
First the GFS. Note how it gets hung up in the south. This is an outlier for now and discounted by the National Hurricane Center (NHC)
The Euro leads the other camp, with a more climatologically normal hook northward as a second trough advances through the eastern U.S. that brings it north and then northeast. On this track, the system is gone by early Sunday.
These depictions will change. They're helpful to illustrate the two camps, but don't tell us a ton forecasting with this much uncertainty. I like using a "super" ensemble, that takes the individual ensemble runs from each of the major global models to identify trends and where things stand.
The image below comes from Tomer Burg's fantastic website.
The image below comes from Tomer Burg's fantastic website.
For now, I don't have much concern about wind. My concern is that we see multiple significant rain events over the course of the week that lead to increased flash flood risk as well as river/stream flooding. Stay tuned as the forecast is fine tuned. The NHC track below reflects the slow movement of Debby. Expect changes as we have more clarity on the longer term track.
The forecast only goes out five days, so it's too soon to see what the NHC thinks about the track next weekend. We don't need to wait however to take action at home.
Right now, I'd recommend making sure sump pumps work, that catch basins and gutters around the house are clear, and if you are in a flood prone area, checking your plans in case there's flooding nearby. It's never a bad time to check your storm kit, either.
The Dailies
Monday: Mostly sunny early with hazy, hot, and humid conditions. Thunderstorms in the afternoon and evening possible, some severe storms possible. Highs in the upper 80s to low 90s. Chance of rain 40%.
Tuesday: Mostly cloudy with rain. Rain may be heavy at times. Highs in the upper 70s to low 80s. Chance of rain 60%.
Wednesday: Mostly cloudy with rain. Rain may be heavy at times. Highs in the mid to upper 70s. Chance of rain 60%.
Thursday: Partly cloudy with rain showers possible. Rain may be heavy at times. Highs in the mid to upper 70s. Chance of rain 40%.
Friday: Mostly cloudy with rain. Rain may be heavy at times. Highs in the mid to upper 70s. Chance of rain 50%
Saturday: Mostly cloudy with rain. Rain may be heavy at times. Highs in the mid to upper 70s. Chance of rain 50%
Sunday: Decreasing clouds, with rain possible early. Rain may be heavy at times. Highs in the mid to upper 70s. Chance of rain 30%
As always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
Thank you for reading SCW.
-DB
Right now, I'd recommend making sure sump pumps work, that catch basins and gutters around the house are clear, and if you are in a flood prone area, checking your plans in case there's flooding nearby. It's never a bad time to check your storm kit, either.
The Dailies
Monday: Mostly sunny early with hazy, hot, and humid conditions. Thunderstorms in the afternoon and evening possible, some severe storms possible. Highs in the upper 80s to low 90s. Chance of rain 40%.
Tuesday: Mostly cloudy with rain. Rain may be heavy at times. Highs in the upper 70s to low 80s. Chance of rain 60%.
Wednesday: Mostly cloudy with rain. Rain may be heavy at times. Highs in the mid to upper 70s. Chance of rain 60%.
Thursday: Partly cloudy with rain showers possible. Rain may be heavy at times. Highs in the mid to upper 70s. Chance of rain 40%.
Friday: Mostly cloudy with rain. Rain may be heavy at times. Highs in the mid to upper 70s. Chance of rain 50%
Saturday: Mostly cloudy with rain. Rain may be heavy at times. Highs in the mid to upper 70s. Chance of rain 50%
Sunday: Decreasing clouds, with rain possible early. Rain may be heavy at times. Highs in the mid to upper 70s. Chance of rain 30%
As always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
Thank you for reading SCW.
-DB
