Good Tuesday Morning. A ton to get to so I'll cut right to the chase.
This morning temps are in the upper 50's to low 60's across the viewing area. It feels pleasant out there with clear skies. There is some patchy valley fog up in The Linville Gorge and around Globe. Today will be our last day in the 80's for a little while. I also think we are very close to not seeing anymore 90° days this year. There could be one or two more here or there but by in large we are heading towards a cooler period.
A cold front is analyzed this morning draped from NNE to SSW orientation from Louisville KY to Cooksville Arkansas. It is making steady progress east on the leading edge of a deep trough. That trough and cold front will be responsible for bringing temps down 10-15 degrees off highs witnessed today. Before the nice airmass change though we have to get through some strong storms. The High Resolution Rapid Refresh Model indicates storms going up across the area around 2pm. We agree wth this scenario and will introduce showers developing across the foothills between 2-3pm. CAPE (Atmospheric energy) is proved to be around 1500 j/kg. I Lehman terms, there is enough energy to allow storms to become fairly strong. Models also indicate some type of meso-low developing just to our North as the cold front approaches. If this does occur then it will enhance thunderstorm coverage after 6-8pm. Sheer (turning of winds with height or speed differences with height) values depend on the eventual development of of that meso-low. It appears enough sheer would be present to support a couple of microbursts from roughly I-40 North. Another round of storms could move in with the front during the early morning hours on Wednesday. Some model guidance is slower with this and don't bring that line of storms in until midday Wednesday. We will narrow that down later today. Rainfall could be very heavy with this front but it will be in a fairly narrow band so we don't expect any kind of flooding issues other than maybe some pounding of water on the roads.
Now we talk about the elephant in the room. There is no ignoring that models continue to show impacts to our area from Irma. Let me first say I caution anyone and everyone to take single model runs with a grain of salt right now. It's our job to generate a forecast looking at all the model data, not just one possible outcome. As of 7am the center of Major Category 5 Hurricane Irma is located about 150 miles to the NE of the lesser Antilles. Here is The National Hurricane Center's 5:00am briefing.
IRMA BECOMES AN EXTREMELY DANGEROUS CATEGORY 5 HURRICANE... ...PREPARATIONS SHOULD BE RUSHED TO COMPLETION IN THE HURRICANE WARNING AREA...
SUMMARY OF 800 AM AST...1200 UTC...INFORMATION ----------------------------------------------
LOCATION...16.7N 57.7W ABOUT 270 MI...440 KM E OF ANTIGUA ABOUT 280 MI...445 KM ESE OF BARBUDA
MAXIMUM SUSTAINED WINDS...175 MPH...280 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...929 MB...27.44 INCHES
Irma is now just showing off in The Atlantic and her structure is one of the best I have seen in a long time. It's crazy how a thing of such beauty can be so deadly and do so much destruction. Category 5 is the highest rating given to a Hurricane. Winds of 175mph. For perspective Harvey's winds were 130mph at landfall and you see the damage he did. We are fairly confident now in a track that takes Irma through the Florida Straight, just to the North of Cuba. The eye of Irma should be between Cuba and Florida by Sunday Morning. From there the model guidance is still very far and very wide. So it stands to reason that we could still see a significant shift in the operational model runs track with Irma. Nothing is set in stone with this storm. There isn't any denying though that the possibility of impacts locally are real. It's still,too early to be specific though on exactly what could transpire here. We think that any impacts locally would hold off until late Monday into Tuesday. So let me set the picture up. All the moving pieces to this puzzle are
2). Bermuda High
3). Eastern US trough
4). Cut off upper level low over Louisiana
5). High pressure ridge over The Great Lakes
6). Cold Air Damming Event East of the Blue Ridge
Models seem to be handling the Bermuda high very well. It's pretty strong at this point and Irma is being steered around that high pressure's southern flank. There is high confidence for that movement to the West to continue based off that high pressure. That will take Irma to the Florida Straight by Sunday Morning. Then she slows. From there a ton of players are introduced onto the ball field Sunday Morning. The trough that is moving into our area tomorrow (behind the cold front that is moving into our area today) should be lifting to the Northeast missing Irma, leaving her behind. So she could still be moving slowly due West. Then on Sunday Night a upper level low cuts off from the main jet stream to the North. Irma could see this opening and that is what we believe could turn her movement to the NNW. We are fairly certain that Irma will impact Florida. Even with Irma in The Florida Straight tropical storm force winds would already be impacting Miami to The Everglades. As Irma sees the opening caused by the cut off low, she will start NNW. Now coming onto the ball field is High Pressure, which is centering over The Great Lakes. Now the question is how much this high pressure has worked out and how strong it is. Irma should be coming North by Monday Morning somewhere between The Gulf Of Mexico and The Atlantic, with Florida being the center point of that cone. The truth is we just don't know the strength of that high or the weakness of that upper low yet. Here is what the models are telling us though. Most of them indicate Irma turning due North and speeding up. I agree with the Northern turn but the speed I have some reservations about. With high pressure ridding down the Easter slopes and becoming stronger over the Great Lakes, also the Bermuda High strengthening, as well as the placement of the upper level low over LA by Monday, it just doesn't seem feesable for Irma to speed up. So that is why there are still some timing issues. The other thing is does Irma come up Florida's West Coast, up throuh Central Florida, or up Florida's East Coast? We don't know. So here are our goals for today as meteorologists.
1). Observe new data from aircraft recon missions
2). Observe new data from weather balloon launches today
3). Work on a track on Irma through or by Florida
4) observe model trends through 00z (7pm EDT)
5). Work on possible impacts to local forecast area
6). Meet with Emergency Management Officials
Here are some things for you to do today while we work on the forecast
1). Gather materials for and emergency kit. These are listed in a graphic below. You should always have an emergency kit handy.
2). Sit down with your family without cell phones and have everyone's attention. Discuss with your family what to do in an emergency situation. Outline Meeting places in case you have to leave the house in an emergency. Don't use trees, mail boxes, cars, etc to meet at. Use something like where the driveway meets the road.
3). Do not panic. The worst case scenario here is not the end of the world. We have survived worse. The threat for injury to yourself or property will be much less if you just take some time to prepare.
4). Monitor later forecasts as the track of Irma could still change significantly.
Category 5 Hurricane Irma 175mph winds. Image at 7:00am 9/5/17
Official National Hurricane Center Track as of 5am 9/5/17
Emergency Prepardness Kit Checklist
Irma Key Messages 8am 9/5/17