Good evening from Southern Connecticut Weather.
For the second time in less than a week, a hurricane is poised to strike the United States. In between my 5pm Facebook post and the time of this update, Hurricane Isaias began to intensify. Currently Isaias is on a northwest heading in the Bahamas with maximum sustained winds of 80 mph. The hurricane will make a close approach or landfall in Florida on Sunday.
The Hurricane Hunters in the storm are finding lower pressures and slightly higher winds. This was expected, but we are closely watching everything that is happening in the Bahamas because any deviation in track or intensity could have a significant impact on what happens here.
For the second time in less than a week, a hurricane is poised to strike the United States. In between my 5pm Facebook post and the time of this update, Hurricane Isaias began to intensify. Currently Isaias is on a northwest heading in the Bahamas with maximum sustained winds of 80 mph. The hurricane will make a close approach or landfall in Florida on Sunday.
The Hurricane Hunters in the storm are finding lower pressures and slightly higher winds. This was expected, but we are closely watching everything that is happening in the Bahamas because any deviation in track or intensity could have a significant impact on what happens here.
Above: the current National Hurricane Center forecast track and the most recent satellite image of the hurricane. During the part of the day where thunderstorm activity is expected to wane, we see deep convection fire right over the center (left burst of white). This is a sign of intensification.
The NHC track is a little closer to the coast than prior tracks, and as you can tell by the cone forecast, confidence decreases in the longer term.
Overall Setup
Steering environment
In the broadest sense, the general steering pattern is straightforward. There is a strong ridge in the Atlantic that is steering Hurricane Isaias in the Atlantic. With a stronger ridge, Isaias would travel further west and into Florida. However, there is a trough in the Midwest that is expected to push toward the east coast, and that will create a weakness in the ridge that allows Isaias to shoot up the coast. As you will see below, the interaction is the key to the eventual specifics of the track, but overall we have more confidence today in impacts in Connecticut.
Development environment
All day, Isaias struggled with wind shear. That both injected try air into the hurricane and disrupted efforts to organize. That shear has not been successful however, as Isaias took all day but finally developed an inner core that will allow it to strengthen. Now that intensification is occurring, we need to watch how resilient the core becomes.
The environment is not entirely favorable for strengthening. There is wind shear that is expected to increase, and a lot of guidance weakens the hurricane as it gets close to Florida. However, as it moves up the coast, if it is over water there is a lot of fuel for some reorganization. The shear may become more favorable as well, and this is something we need to watch. Overall however, this should make a landfall along the Carolinas, and that will cause weakening.
The NHC track is a little closer to the coast than prior tracks, and as you can tell by the cone forecast, confidence decreases in the longer term.
Overall Setup
Steering environment
In the broadest sense, the general steering pattern is straightforward. There is a strong ridge in the Atlantic that is steering Hurricane Isaias in the Atlantic. With a stronger ridge, Isaias would travel further west and into Florida. However, there is a trough in the Midwest that is expected to push toward the east coast, and that will create a weakness in the ridge that allows Isaias to shoot up the coast. As you will see below, the interaction is the key to the eventual specifics of the track, but overall we have more confidence today in impacts in Connecticut.
Development environment
All day, Isaias struggled with wind shear. That both injected try air into the hurricane and disrupted efforts to organize. That shear has not been successful however, as Isaias took all day but finally developed an inner core that will allow it to strengthen. Now that intensification is occurring, we need to watch how resilient the core becomes.
The environment is not entirely favorable for strengthening. There is wind shear that is expected to increase, and a lot of guidance weakens the hurricane as it gets close to Florida. However, as it moves up the coast, if it is over water there is a lot of fuel for some reorganization. The shear may become more favorable as well, and this is something we need to watch. Overall however, this should make a landfall along the Carolinas, and that will cause weakening.
The Guidance
Overall, today's guidance has shifted the track of Isaias further west. The good news with that is it increases the likelihood that land interaction in the southeast weakens the storm substantially. The bad news is that it makes is more likely that this goes up the East Coast without going out to sea.
The guidance does not bring Isaias up to the New England region as a hurricane. However, it does make a close approach on most guidance as a moderate to strong tropical storm. Again, this can change and change quite a bit depending on what happens down south.
We are not yet confident enough in the overall evolution to provide specific details on local impacts.
We will however, provide a broad overview of possible impacts.
Overall, today's guidance has shifted the track of Isaias further west. The good news with that is it increases the likelihood that land interaction in the southeast weakens the storm substantially. The bad news is that it makes is more likely that this goes up the East Coast without going out to sea.
The guidance does not bring Isaias up to the New England region as a hurricane. However, it does make a close approach on most guidance as a moderate to strong tropical storm. Again, this can change and change quite a bit depending on what happens down south.
We are not yet confident enough in the overall evolution to provide specific details on local impacts.
We will however, provide a broad overview of possible impacts.
Above: The 12z European Ensembles, courtesy of weathermodels.com. As you will see, virtually all of the ensemble members connect the lines in the Bahamas (current location of Isaias) and track it up the coast. All those projections bring impacts to CT, which increases our confidence that impacts will occur.
Possible Scenarios & Impacts
As I see it, there are three outcomes possible. This could be stronger but further offshore. It could be weaker but closer to CT. It could also scoot east at the last minute and give us a glancing blow.
Scenario 1: Weaker but closer to CT
Under this scenario, the current National Hurricane Center forecast more or less pans out. Hurricane Isaias weakens along the Florida coast and makes a landfall in the Carolinas. It weakens over land, but makes a closer approach to CT, with the center likely passing just SE of CT on Tuesday. This would bring heavy rain and some gusty winds, especially near the shoreline. This would be an impactful event, especially in SE CT and places where rain bands set up. This is currently the overwhelming favorite.
Chance of occurrence: 65%.
Scenario 2: Stronger but further offshore
Under this scenario, Isaias is slightly to moderately stronger than anticipated after making a landfall in the Carolinas. This could happen in two ways. First, the storm could intensify more than expected tonight and tomorrow, and ends up hitting land stronger. This would mean that the system takes longer to weaken. The second way would be that the system while over land is enhanced by the trough that it is interacting with. The result would likely mean that the system is further east, but it increases the heavy rain and wind threat, especially in southern CT. This is possible, but not terribly likely at this time.
Chance of occurrence: 25%
Scenario 3: Last minute swing east
Under this scenario, the trough orientation and speed makes it more of a "kicker" than enabler, forcing Isaias offshore faster and delivering a glancing blow or no impacts. This is highly unlikely at this point, but I am introducing this option in case there is an undersampling in the guidance that has taken place. We should know how viable this is after the set of model runs tonight as they take in new data from the hurricane hunters. As you can see, I wouldn't count on it.
Chance of occurrence: 10%
Timing
We are looking at Tuesday being the most likely time that we see impacts from a weakened Isaias.
Overall
To sum things up, we have increasing confidence that a weakened Isaias will run up the coast and bring us impacts. The extent or severity of the wind and rain is not known at this time. This does not currently look like a highest end event, but this is something to take seriously. We will be back with additional updates daily as we receive more information and begin crafting a storm specific forecast.
If you haven't already, now is the time to check your supplies, check your generator if you have one, and prepare to purchase supplies if this looks like a higher impact event tomorrow.
Stay tuned.
Possible Scenarios & Impacts
As I see it, there are three outcomes possible. This could be stronger but further offshore. It could be weaker but closer to CT. It could also scoot east at the last minute and give us a glancing blow.
Scenario 1: Weaker but closer to CT
Under this scenario, the current National Hurricane Center forecast more or less pans out. Hurricane Isaias weakens along the Florida coast and makes a landfall in the Carolinas. It weakens over land, but makes a closer approach to CT, with the center likely passing just SE of CT on Tuesday. This would bring heavy rain and some gusty winds, especially near the shoreline. This would be an impactful event, especially in SE CT and places where rain bands set up. This is currently the overwhelming favorite.
Chance of occurrence: 65%.
Scenario 2: Stronger but further offshore
Under this scenario, Isaias is slightly to moderately stronger than anticipated after making a landfall in the Carolinas. This could happen in two ways. First, the storm could intensify more than expected tonight and tomorrow, and ends up hitting land stronger. This would mean that the system takes longer to weaken. The second way would be that the system while over land is enhanced by the trough that it is interacting with. The result would likely mean that the system is further east, but it increases the heavy rain and wind threat, especially in southern CT. This is possible, but not terribly likely at this time.
Chance of occurrence: 25%
Scenario 3: Last minute swing east
Under this scenario, the trough orientation and speed makes it more of a "kicker" than enabler, forcing Isaias offshore faster and delivering a glancing blow or no impacts. This is highly unlikely at this point, but I am introducing this option in case there is an undersampling in the guidance that has taken place. We should know how viable this is after the set of model runs tonight as they take in new data from the hurricane hunters. As you can see, I wouldn't count on it.
Chance of occurrence: 10%
Timing
We are looking at Tuesday being the most likely time that we see impacts from a weakened Isaias.
Overall
To sum things up, we have increasing confidence that a weakened Isaias will run up the coast and bring us impacts. The extent or severity of the wind and rain is not known at this time. This does not currently look like a highest end event, but this is something to take seriously. We will be back with additional updates daily as we receive more information and begin crafting a storm specific forecast.
If you haven't already, now is the time to check your supplies, check your generator if you have one, and prepare to purchase supplies if this looks like a higher impact event tomorrow.
Stay tuned.
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Thank you for reading and trusting SCW.
-DB
Thank you for reading and trusting SCW.
-DB
