Tropical Major Hurricane Irma (Part 1)

[Webberweather53]

I agree. Even if the 12Z Euro verified closely and it got that far west, it would very likely later recurve between 70 and 75 W as per what the 12Z EPS shows as the E US trough doesn't appear to be going away quickly. The WAR wouldn't be able to dislodge the trough per the EPS mean, with which I agree. Instead, its westward move comes to a halt just after day 10.

This is from an analysis I did awhile back:

2) 1960-2002 (with wx satellites):

a) I counted 21 CONUS hits from 125 storms that first became at least a TD east of 50W and south of 20N, which means the hit % for these was 17% or about one in six.

b) Of these 125 storms, 85 first became at least a TD east of 40W. Out of those 85, I counted 14 that hit the U.S., making the hit % for those which first formed east of 40W near 16% or just under one in six (i.e., not much different).

From another study I did awhile back:
The % U.S. hit rate for each month of formation of TCs East of 50W and S of 20N was as follows: 0% for each of June, Oct., and Nov.; 25% for July, 26% for Aug., and 17% for Sept. So, a C.V. STORM THAT FORMS DURING AUG. HAS A PRETTY SIGNIFICANTLY HIGHER CHANCE TO HIT THE U.S. ( ABOUT 1 IN 4) THAN ONE THAT FORMS DURING SEPT. (ONLY ABOUT 1 IN 6). July is also relatively high like Aug.

93L is progged to become a TD either in very late Aug or very early Sep. So, I'd call its chances of hitting the CONUS about 1 in 5 (splitting the difference) if ignoring models. Being in cold neutral to possible weak Nina probably doesn't sway the chances too much. Had it been mod to strong Nina, the chances would be raised while lowered for Nino.

Since the models are pretty strongly favoring a recurve E of the CONUS, I think the odds are probably a bit lower than 1 in 5....say something like 1 in 7 as of now. That's my take anyway.

FSU performed an observational study an all BEST track data and calculated the probability of a TC making landfall in the US from any given location in the Atlantic.
From 93L's current location, it has about a 15% chance of making landfall in the US. If it were to reach the location just north-northeast of Puerto Rico shown by the day 10 Euro, those chances nearly triple to about 40%...

 

[GaWx]

^ Nice map! The 15% is near my numbers. Even if it were to get to that position just NNE of PR on day 10, its odds of hitting the US imo would be a good bit lower than 40% based on the progged strong/persistent E US trough on the Euro/EPS. I look at the 40% as incorporating all sorts of scenarios from favorable stable or moving west WAR that may extend into the E US to unfavorable persistent E US troughing.

 

[GaWx]

I said further east ... - just want to keep everything away from our back yard, Larry (power of positive thinking ... ), and very eastern NC got flooded, so something more east that gives NC some non-flooding rain may not be a bad thing ...

I agree with you now. You hadn't yet added the "further east" when I quoted you. Please no Floyd-like scares. Floyd was a close call and a big scare to FL/GA/SC causing millions to have to evacuate out of precaution even though only its weak side hit there. Even its weak side packed a punch as it was large. But that wasn't the problem here. It was the huge traffic jams from evacuations though I went very late and didn't have it that bad.

 

[Metwannabe]

I agree with you now. You hadn't yet added the "further east" when I quoted you. Please no Floyd-like scares. Floyd was a close call and a big scare to FL/GA/SC causing millions to have to evacuate out of precaution even though only its weak side hit there. Even its weak side packed a punch as it was large.

Floyd was a disaster for NC coupled with the heavy rains received from Dennis just a few weeks prior, no NO Floyd please... I tell my dad all the time Floyd was my generations Hazel (he always tells me about Hazel, an entirely different beast with significant wind damage)

 

[pcbjr]

I agree with you now. You hadn't yet added the "further east" when I quoted you. Please no Floyd-like scares. Floyd was a close call and a big scare to FL/GA/SC causing millions to have to evacuate out of precaution even though only its weak side hit there. Even its weak side packed a punch as it was large.

Yeah - I edited before your post appeared ... sorry for the miscommunication ...
And yes, Floyd had some nerves spiking down here - which was not my message ...
I meant to suggest something to watch but not to deal with ...
Perhaps I need to go to writing class ...

 

[Brent]

GFS trending toward a weaker trough this run but we'll see what happens

Recurves between Bermuda and the OBX around day 14

 

[Brent]

The Euro looks fun, almost looks to be moving south of west approaching the Antilles, plenty of ridging in front

 

[Brent]

192 hours major hurricane moving into the Caribbean way south of the last run

 

[Brent]

:weenie::weenie:

 

[Brent]

:weenie::weenie::weenie::weenie:

 

[Webberweather53]

^ Nice map! The 15% is near my numbers. Even if it were to get to that position just NNE of PR on day 10, its odds of hitting the US imo would be a good bit lower than 40% based on the progged strong/persistent E US trough on the Euro/EPS. I look at the 40% as incorporating all sorts of scenarios from favorable stable or moving west WAR that may extend into the E US to unfavorable persistent E US troughing.

I don't think we can necessarily make the determination yet that its chances are below climatological normals and that the trough will actually still be there by the time 93L reaches the edge of the WAR in the SW Atlantic... In fact, after day 8-9 the EPS show this positively tilted trough getting strung out and lifting as the WAR already extends nearly to the eastern seaboard and its trying to rebuild and bridge with the ridge over western North America to the north and northeast of 93L...

 

[Webberweather53]

ECMWF ensemble track density guidance for 93L. Showing a fairly pronounced and somewhat unusual WSW motion in the central Atlantic w/ the heaviest clustering taking it near/just north of PR and towards the southeastern Bahamas after day 10...

 

[Webberweather53]

93L is organizing nicely this morning and is well on its way to becoming a tropical depression, with a deep, consolidated convective burst near the center of the sharp-very sharp wave axis. Recent ASCAT pass, which showed the northernmost portion of the wave, revealed 93L has a deep envelope of earth relative westerlies to the south thanks in large part to current MJO juxtaposition over the Indian Ocean and its connection to the monsoon trough and the concomitant monsoon southwesterlies...

 

[Webberweather53]

93L might actually be in a position where the eastern US trough, spurred by the recurvature of Sanvu in the western Pacific, actually helps induce this west-southwest motion in the central Atlantic by amplifying the Azores-Bermuda high downstream... This sort of behavior is extremely rare and I can only find a few examples of this in the last century or so & of these storms all of them hit landmasses further W in some way, shape, or form. NWP skill wrt the planetary wave configuration downstream of the West Pac is notoriously bad after these typhoon recurvatures and they (esp the GFS/CMC) tends to underestimate this WSW motion underneath a burgeoning subtropical high...

 

[Webberweather53]

NHC raising the odds of development to 90% in 5 days, looks like this will eventually become Irma...

1. Showers and thunderstorms associated with a low pressure area near
the Cabo Verde Islands have become better organized since yesterday.
Environmental conditions are conducive for development, and a
tropical depression is expected to form in 2 or 3 days over the
eastern Atlantic. The low is forecast to move generally
west-northwest at 15 to 20 mph over the tropical Atlantic during the
next several days. Heavy rain is possible over portions of the Cabo
Verde Islands through Wednesday.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 5 days...high...90 percent.

 

[Webberweather53]

93L might actually be in a position where the eastern US trough, spurred by the recurvature of Sanvu in the western Pacific, actually helps induce this west-southwest motion in the central Atlantic by amplifying the Azores-Bermuda high downstream... This sort of behavior is extremely rare and I can only find a few examples of this in the last century or so & of these storms all of them hit landmasses further W in some way, shape, or form. NWP skill wrt the planetary wave configuration downstream of the West Pac is notoriously bad after these typhoon recurvatures and they (esp the GFS/CMC) tends to underestimate this WSW motion underneath a burgeoning subtropical high...

We can also add Karl (2016) to this list...

 

[Webberweather53]

New ASCAT pass reveals 93L has a closed yet very broad, zonally elongated circulation atm, likely will take a few more days for it to consolidate into a tropical depression and/or Tropical Storm Irma.

 

[GaWx]

93L might actually be in a position where the eastern US trough, spurred by the recurvature of Sanvu in the western Pacific, actually helps induce this west-southwest motion in the central Atlantic by amplifying the Azores-Bermuda high downstream... This sort of behavior is extremely rare and I can only find a few examples of this in the last century or so & of these storms all of them hit landmasses further W in some way, shape, or form. NWP skill wrt the planetary wave configuration downstream of the West Pac is notoriously bad after these typhoon recurvatures and they (esp the GFS/CMC) tends to underestimate this WSW motion underneath a burgeoning subtropical high...

I agree that any WSW motion should set off alarm bells. I did a study a number of years ago that showed that a fully developed TC moving WSW in the eastern MDR correlates to a higher than normal chance to hit landmasses in the western basin.

 

[WeatherWatch]

Yes, I agree, we won't know if that trough will still be over the east as 93L approaches closer to the EC. At the moment, there's more questions than answers. Will the trough still be over the east? It could, then again, the trough may lift out allowing 93L to have more of a chance at putting a threat along the EC. Or, 93L may very well just ride along the side of the Atlantic ridge and OTS it goes. Maybe 93L will stay in the lower latitudes and come on the back side of the trough as the trough is lifting, if that was the case 93L would be a GOM threat. At this point, we just won't know. More answers will come as the days progress. Also, that observational map from FSU that Webber posted. That's a really good map, I saved that map for future reference.

 

[GaWx]

The 12Z GFS is a totally different scenario with a much weaker TC crossing much further south and which opens up near PR while the E US trough lifts out more quickly. The end result is a very weak low or wave that moves into S FL on 9/11 from Cuba and then recurves just offshore the SE US moving ne 9/13-4.

The 12Z GEFS mean agrees with the 12Z GFS on the weaker and further south track though it doesn't have the E US trough moving out more quickly like the 12Z GFS has.