Friday, Sept. 8, 2017

Irma down to a strong Category 4

Worst-case scenario coming into focus

At this point, it is mostly a case of waiting and waiting.  Forecast models have converged into a pretty strong consensus.  The only lingering question is how strong she’ll be at landfall?

After mostly giving up on the west coast (of Florida) solution on Wednesday, the models came roaring back yesterday.  Today, most of the holdouts have joined the chorus.  Irma will hit land over southwestern Florida Sunday morning and continue slowly north over the state for at least 24 hours.  Of the various ideas suggested by the models this week, that’s the “worst case scenario.”  And, now that’s the solution that seems to be most likely.

We can now be pretty confident  as to the where and when of landfall, but the strength remains a question.  NHC has it still with winds of 145 mph at landfall.  I feel that estimate is too high because from now until landfall its circulation will be affected by land masses.  That will disrupt the storm enough to weaken its winds by at least 10-15 mph.  That’s the low end of Cat 4, but Cat 3 is still a possibility.  Even with reduced winds, this storm is very bad news for Florida.

6 P.M. Thursday, Sept.7.2017

Trend highlighted in earlier post today is now showing up strongly in latest GFS output.

Idea of landfall Sunday morning over southwest Florida is looking more and more likely.  If trend continues, it’s VERY bad news for Florida.  Latest NHC update is starting to incorporate these ideas.

Thursday, Sept.7, 2017

Models shift a bit…looking worse for Florida

Model solutions converge as U.S. landfall gets closer.  However, an old model idea is regaining favor and that, if it happens, could be really bad news for Florida.  More on that later.

First, The official National Hurricane Center’s forecast track has shifted a little westward from yesterday.  That’s in line with the model consensus which tracks Irma either along, or just east of Florida’s east coast.   A similar storm last fall followed this path and Florida fared pretty well.  Irma is stronger, however, so this path would create more problems this time around.

Following that path, landfall would occur somewhere around the GA/SC coast.  That area would have the highest risk of devastating winds/storm surge.

The current forecast follows the path described above with Irma either over Miami or just off the coast by about 7-8 P.M. Saturday, slowly moving north overnight and Sunday.  During this time it is expected to be either a strong Category 4 or Category 5. (winds 145 mph or higher).  Landfall would occur Sunday night near the GA/SC border.

New thoughts:

While the above remains the official forecast, I’ll wait awhile before I totally agree.  Tuesday, I mentioned that the forecast models fell into two camps.  One brought Irma up the Florida east coast; the other took it inland over the Gulf side.  That idea disappeared yesterday as the models shifted to a more easterly path.  Today, several models have brought back that idea, in what amounts to a very ugly way.

Hurricanes are purely tropical systems, but as they approach North America and recurve (turn) northward mid-latitude wind systems also get involved in the steering mechanism.  Our current cool weather has arrived do to an unseasonably strong upper level trough digging into eastern North America.  Apparently, yesterday the models felt the trough was stronger (and slower) than it actually is.  The result was to predict the storm path farther east.  Today, however, the models have corrected yesterday’s overreach.  That greatly reduces the trough’s ability to encourage Irma to turn northeast over the weekend as mid-latitude winds will become very weak.  How does that change things?

The models predicting the movement of Irma into the Gulf have also slowed her speed, probably due to the relaxing of the wind fields over the U.S.  They have also delayed the northward turn.  The result is Irma drifting between Florida and Cuba Saturday night, then turning northward Sunday into southwest Florida.  Furthermore, the delay will allow steering currents to weaken even more.  As a result, this model idea would allow a dying Irma to remain over Florida 24-36 hours!  You don’t even want to think about that scenario.

I’m hoping the models will present a clearer picture by tomorrow.  I’m also hoping that the current NHC prediction is very close to correct.  If it isn’t and the slower developing idea wins out, Irma will become a name we’ll remember for a long, long time.

Personally, I’m getting very worried about Florida.

Wed. Sept. 6, 2017

Models change:  better prospects for Florida

Today’s model runs are shifting the path of Irma slightly north and the expected turn north a little sooner.  That adds up to slightly better news for residents of Florida.  Most models now have Irma hugging the Florida east coast Saturday night and Sunday.  That path would still create huge problems for the coast, but not as much as a direct hit would.

Florida’s slightly better news means worse news for Georgia and South Carolina.  Model consensus now puts landfall near the GA/SC border late Sunday.  Irma should still be a major hurricane so that area could well bear the brunt of the winds/storm surge.

Beyond that, a weakened Irma is expected to diminish while spreading tropical rains northward along the Atlantic Coast (mostly east of the Appalachians).

Other model ideas:

There is pretty good model agreement up to about 3-4 days.  After that, two models offer “outlier” solutions.

First, the Canadian model is much farther east than the consensus.  It keeps Irma far enough east of Florida’s east coast to ease the coastal erosion significantly.  Irma then brushes by the Outer Banks.  Later, a much weakened Irma could make landfall near Cape Cod.  At the moment, that’s the best case scenario for the U.S.

Second, the GFS continues to hang on to its ideas mentioned yesterday.  And, it is faster than the other models by 12-24 hours.  It is the only model to push the remnants of Irma northwest. It still pushes the dying storm over the lower Ohio Valley by Tue/Wed.

Those two model ideas sum up the frustrations facing forecasters every day.  The farther you try to look into the future, the more the uncertainty increases.   Two reliable models (for the short term), starting out with the same data, predicting the same major storm’s path.  At 6-7 days time, one has the parent system over western KY and the other has it near Cape Cod.  Go figure?

My ideas:

History has shown me that once a hurricane track forecast changes to a more easterly path, that trend usually continues.  And, very little forecast path change is likely in the 48 hours leading up to landfall or near miss.

With this in mind, I believe that by tomorrow morning (Thursday) the model consensus will continue to shift eastward.  Not as far as the Canadian, but in that direction.  By Friday, the forecast will be pretty well “locked in” with only minor adjustments after that.

Thus, I expect Irma will not make a direct hit on Florida.  East Florida will suffer from high surf and beach erosion, but problems will be minor to what a direct hit would create.

As Irma heads NNE, I expect the North Carolina coast to be hit hard.  It’s possible it could only be the Outer Banks area, not the whole coast.  After that, I don’t even want to speculate.

Stay tuned, by tomorrow we could have a whole set of new ideas!

10:30 A.M. Wed., April 5, 2017

Atmosphere appears set up to do some damage later today – especially east of the I-65 corridor.  Strong upper air system is approaching and ample moisture is streaming northward.  That sets up a pretty high chance for thunderstorms as well as severe storms.  System will be slow to develop and will just be getting rolling about the time it hits central KY.  Strong/severe line of storms should pass Louisville area between 5 P.M. and 8 P.M.  Hail and high winds appear likely.   Storm line will intensify as it moves east of I-65 and heads toward I-75.  Also, higher risk for storms, some severe, over southern KY from I-65 eastward.

Much colder air arrives tomorrow.