Joe’s Weather Blog: What we know and don’t know about Florence (WED-9/12)

I’m going to try to simplify things a bit with this weather blog because now, as I told you last week…Florence has become the biggest news story of the week and the biggest weather story of the year. There are now some curve balls being thrown from Florence…and one of the biggest ones is where will Florence come inland and stay inland. That is actually becoming an unknown right now. A couple of days ago I was focusing some information on the Wilmington, NC area…and that, to me still seems relevant BUT all the momentum of the storm now (moving at close to 15 MPH) will be fading as the storm tries to come ashore…as a result now we may be looking at a storm that hugs the coastline…perhaps shifts and moves farther towards the SW (unusual) and wallows around for 2 days near the Carolinas.

There are obvious longer term (3-6 day)) issues with these possibilities. II have a feeling that we really won’t have a strong feel for a possible landfall till later tomorrow as we judge the forward speed and see if it has enough momentum to barrel ashore.

Back home in KC…no real changes and very little to no rain coming…perhaps a random shower here or there over the next 7 days…but nothing concrete to hang your hat on…just a persistent pattern of warmth and dry weather (mostly) for the next 10+ days it appears.



Forecast:

Today: Sunny with some clouds around and highs in the lower 80s

Tonight: Fair and pleasant with lows in the 60s

Thursday: Same but you may start to notice the humidity creeping up a bit with highs well into the mid 80s

Friday: A bit more muggy too with highs 85-90°



Discussion:

Now it’s time for the curveballs and the data last night is indeed throwing some interesting adjustments into my thinking. Here is what we know.

Florence is still a major hurricane.

It’s been vacillating in strength from 130-140 MPH for the last 24 hours or so. It’s a potent storm…no doubt about it but it may never make category 5 strength despite favorable water temperature conditions and a favorable atmospheric set-up. These two factors may well change though later Thursday into the weekend for the storm’s “health”

Here’s one of the questions about the storm…as the steering currents collapse as the storm comes near the coast will it even come ashore?

There is a “weird” phenomena that I’ve noticed over the past years with slow moving hurricanes. They sometimes avoid coming onshore. It’s almost as if the land repels the storm’s core. I’m not sure there is a scientific reason for this…perhaps it has to do with frictional effects of the storm’s circulation and land interacting with each other. I’ve noticed this with storms that “wobble” unexpectedly as they try to come ashore in the northern reaches in the Gulf of Mexico too.

Also…as this happens with crawling storm motions the hurricanes circulation starts getting disrupted because about half the storms circulation is over land…and removed from the water and the better “gas” for the hurricane engine.

The EURO model and to some extent the GFS model are showing these weird motions to the storms arrival ashore.

The GFS model which is still suffering from over-strengthening the storm’s core has this look for Friday afternoon.

Remember the worst part of a hurricane are towards the north and northeast of the storm’s center…so this would be a coastal onslaught for areas near and north of Wilmington, NC.

Now look at the forecast from the GFS for 24 hours later

Notice the SW movement of the storm…as if it’s trying NOT to come ashore. Now the worst onslaught of surge and wind is drifting towards the south…towards the far south part of NC…and not SC is coming more into play.

With such a slow storm motion…as the winds churn up the waves…and we’re talking 20-40 foot monster waves near and offshore…the waters will be “upwelled” and the surface waters will cool down rather significantly.

This will alter the “premium” gas for the storm’s engine to something that would be less than “regular” gas. This will be an issue for the storms health. That plus the half the storms circulation being over land is not a good thing for a storms “engine”.

There is another issue that some but not many meteorologists are NOT talking about…as the storm comes closer to land, especially starting on Friday…wind shear will start ripping at the storms circulation…and that may be a bigger issue in the long run for the storms health.

I’ve had my suspicions that it’s been undergoing some shear since yesterday because, at times the satellite presentation of the storm’s core looks a bit ragged. Well this shear is forecast to increase more.

One model that shows this is called the SHIPS model. There is a lot of mumbo jumbo on the next model output but I’ve highlighted two lines for you…one is the time line…starting 60 hours into the future which on this computer run would be later Friday afternoon/evening…and the wind shear ripping at the storm. Under 10 knots of shear is doable for a storm…over 20 kts…is a different thing and this too will toy with the storm’s health I think.

So sometime on Friday…especially later in the day…assuming the storm is near or off the coast…we’ll have a storm that will be feeling the effects of having half the circulation over land…waters that are being churned and upwelled because of the wave action…and increasing shear ripping at the storms structure. All reasons for a storm that should lose, at least some of it’s punch.

Now the problems…and there are many.

The storms slow movement, regardless of where it goes means some of the coastal areas…large swathes of the NC coast…will undergoes high and low tides and storm surge waters together for a prolonged period of time. For most landfalling hurricanes…it’s one tide cycle…either high tide (worse) or low tide (better)…this may be a couple or more. That increases the erosion on the beaches and just because a hurricane may weaken dramatically in the wind department…it takes time for the wave action to start dropping off…in other words the strong winds drop but there is a lag of waves/surge dropoffs. We saw this with Katrina…the winds dropped significantly as it came ashore but there was so much water built up and moving that that aspect didn’t drop off.

Rainfall…who exactly gets the most…well there are some adjustments that need to be thought about…and for parts of NC perhaps some good news…but for parts of NC and SC perhaps some bad news…

Here is the EURO portrayal.

Repeated bands of heavy tropical rains stream ashore from the circulation as it wanders near the coastline…this brings the worst flooding more towards the eastern part of the state and actually helps the western part of the state compared to a few days ago. This would reduce the “lifting” in the mountainous areas for at least several days and refocus the worst flooding towards and near the coastline.

Notice how even GA comes into play.

Just the shear amount of water falling from the skies with this will be incredible.

How are we getting data to input in the models to help us with this forecast? Well there are several ways. For the last few days many of the weather offices east of the MS River have been sending up two extra weather balloons each day. Typically these go up at 7AM/7PM…but now there are additional ones at 1PM and 1AM. This extra atmospheric information is fed into the the model data.

In addition one of the best ways is through recon data. Airplanes fly around the circulation and through the circulation gathering data. They actually release dropsondes that fall through the outer circulation of the storm to get an idea of the atmosphere around the storm. Here is an image from the recent recon this morning…look for all the “pipe-looking” objects on the map…those are the dropsondes going down towards the surface from the flight level of the aircraft.

The plane left FL and is returning to FL as of 8:25 AM this morning (CDT)

Check out these pictures from a recon flight a couple of days ago as they flew right into the eye of the storm…note when they get there the structure…”stadium effect” of the eye where the are huge clouds…almost like a bowl, around the middle of the storm.

The HOPE is that all this data will result in better model input and better output.

We’ll need it because there are more curveballs coming I think into the weekend with Florence IF those steering currents collapse as expected.

Yesterday we talked about these ERC’s or Eyewall Replacement Cycles. There are more of these coming too…perhaps one today. IF you missed yesterday’s blog…these occur as the hurricane reorganizes every so often. On the plus side the storms winds (at the core) drop off somewhat. On the negative side the storms winds expand to cover a larger area.

Many records may fall from this storm…including pressure records…

Then there are the rainfall records that are in jeopardy with the storm…from VA to GA.

I’ll leave you with this…and this blog has gotten long…

Note the “mesovorticies” spinning around within the eyes structure. This was from yesterday.

OK that’s enough. More on the storm surge impacts tomorrow as the track hopefully is clearer.

Feature photo is from Tedd Scofield (@teddscofield)

Joe

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