2017 Global Model Runs Discussion (Out to day 16)

[RL3AO]

Looks like a pretty classic CAG event. Wouldn't be surprised to see a TC in the EPac and Atlantic.

What's 'CAG' stand for? thanks.

Central American Gyre. It's a monsoon gyre that forms around Central America - most commonly during May and October.

[LarryWx]

I'm going to restate what I have been saying about western ATL basin TC genesis/development GEFS biases as some are not following what I'm saying:

- the 18Z GEFS has day after day been the most active GEFS run BY FAR. A theory has been presented in this thread that this is due to 18Z being the time of max solar insolation in/near the western ATL basin.
- the 6Z GEFS has day after day been the least active GEFS run BY FAR.
- the 0Z/12Z have been in between the surrounding 18Z/6Z every time.

Am I making sense? With a repeating pattern like this, there are obvious biases that need to be considered when looking at each GEFS run as randomness definitely doesn't explain this. When I see the 18Z GEFS, I assume it is too active. When I see the 6Z GEFS, I assume it is too quiet. The 0Z/12Z GEFS seem to be the most reasonable to me of the 4 runs.

[Steve H.]

Maybe for the GFS family this is true. However the Euro has been showing lowering pressures and vorticity in the western Atlantic (Caribbean) for days, so I tend to think it is sniffing something out. It usually doesn't play the phantom cyclone game.

[NotSparta]

Looks like a pretty classic CAG event. Wouldn't be surprised to see a TC in the EPac and Atlantic.

What's 'CAG' stand for? thanks.

Central America Gyre

[SFLcane]

 https://twitter.com/DavidBernardTV/status/912263729500295169

[SFLcane]

 https://twitter.com/webberweather/status/912064694957019136

[blp]

I'm going to restate what I have been saying about western ATL basin TC genesis GEFS biases as some are not following what I'm saying:

- the 18Z GEFS has day after day been the most active GEFS run BY FAR. A theory has been presented in this thread that this is due to 18Z being the time of max solar insolation in/near the western ATL basin.
- the 6Z GEFS has day after day been the least active GEFS run BY FAR.
- the 0Z/12Z have been in between the surrounding 18Z/6Z every time.

Am I making sense? With a repeating pattern like this, there are obvious biases that need to be considered when looking at each GEFS run as randomness definitely doesn't explain this. When I see the 18Z GEFS, I assume it is too active. When I see the 6Z GEFS, I assume it is too quiet. The 0Z/12Z GEFS seem to be the most reasonable to me of the 4 runs.

Larry I appreciate your research on this. I too have seen this trend. I for one am waiting to see how the Euro resolves this. This is the new GFS and I still don't have a feel for its bias in the W. Caribbean. You know the old GFS was typically bias toward over development in the W. Caribbean in the early and late season. I am not sure what to make of this. I think it is very interesting finding and I wonder if this impacts other 18z models that might use the same input data.

I do see the Euro, GFS, CMC, NAVGEM, JMA hinting at something but they all seem to be scattered right now with varying solutions since it is early.

[CyclonicFury]

Looks like a pretty classic CAG event. Wouldn't be surprised to see a TC in the EPac and Atlantic.

What's 'CAG' stand for? thanks.

Central American Gyre. It's a monsoon gyre that forms around Central America - most commonly during May and October.

Don't storms that form like this tend to be sloppy tropical storms rather than well-developed hurricanes?

[LarryWx]

In the western ATL basin during 10/4-9, today's 0Z EPS wasn't as active as yesterday's 12Z EPS though it still had notable activity:

Out of 50 runs, 9 (18%) were Hs vs 10 the prior run and 9 two runs ago. 3 hit W FL as Hs 10/7-8, 2 hit the Bahamas 10/7-9, 1 hit MS/AL 10/7, 1 hit LA 10/9, and the other 2 were still in the middle of the GOM moving slowly N/NW at the end of the run (10/10). I counted ~15 (~30%) TS+ vs ~22 (~44%) TS+ the prior run and ~15 (~30%) TS+ two runs ago.

[AxaltaRacing24]

What's 'CAG' stand for? thanks.

Central American Gyre. It's a monsoon gyre that forms around Central America - most commonly during May and October.

Don't storms that form like this tend to be sloppy tropical storms rather than well-developed hurricanes?

For sure in May and June but at this midpoint in the season, things would be a little different if it formed near the TCHP in the western carib.

[Frank2]

The good news is the GFS also shows strong high pressure to our north during that same time....

[Steve]

The good news is the GFS also shows strong high pressure to our north during that same time....

Which is exactly why you look south or southeast of that for development.

[LarryWx]

The good news is the GFS also shows strong high pressure to our north during that same time....

Frank,
Contrary to what you apparently think, a strong surface high to the north actually can make it more conducive for TC genesis below it. Check out at old weather maps and you'd see examples of this.

[perk]

The good news is the GFS also shows strong high pressure to our north during that same time....

Frank,
Contrary to what you apparently think, a strong surface high to the north actually can make it more conducive for TC genesis below it. Check out at old weather maps and you'd see examples of this.

What Frank may have meant is that high pressure won't allow a TC to move toward Florida we all know that high pressure can aid in TC development.

[CourierPR]

I just viewed the Saturday Summary video on weatherbell.com and Met. Joe Bastardi said he expects development in the W. Caribbean during the first ten days of October according to the pattern setup.

[Tampa Bay Hurricane]

As always, any information from the National Weather Service and National Hurricane Center will supercede anything that I forecast on here. They are the experts, I am still a student.

With that established let's get started. GFS and EURO consistently showing an Atlantic Cyclone long range. EURO develops it in the WCarib. GFS develops it in the Bay of Campeche and brings it NE into the South Central Gulf of Mexico. Some other analogues which occurred during La Nina years are Mitch and Wilma.

October 1-11 will be the time frame to really watch for explosive La Nina favored development in the West Caribbean.

Pressures are lowering and conditions with non-existent shear and near-record high oceanic heat content waters will be favorable for the formation of a powerful hurricane that in my opinion could rival 2005's Wilma as the most intense hurricane ever recorded in the Atlantic.

I say this because Irma set a record as the most powerful hurricane in the Atlantic ever outside of the GOM and Caribbean. Irma also set numerous Cat 5 165-185 mph landfall records.

With this in mind, I think we break Wilma's record in the WCarib this year, since conditions as extra favorable over the Atlantic this year for rapid intensification of developing tropical cyclones, as we saw with Jose, Harvey, Maria, Irma, and other Atlantic cyclones this year.

I think we will also get brief development in the EPAC (Eastern Pacific) before said convectively favorable parameters illustrated by the Madden-Julian Oscillation move into the WCarib (Western Caribbean Sea, including the waters adjacent to Cuba and Mexico's Yucatan Peninsula. So EPAC storm, then the powerful WCarib form.

It is possible that the cyclone may initiate over the SW Caribbean east of Nicaragua or in the central Caribbean prior to being guided into the NW Caribbean.

I wish to reiterate that the forecast in this post is a purely academic endeavor, based purely on my study of the subject of tropical meteorology of the Atlantic Ocean, and should not supercede any information given by the National Hurricane Center.

Please do not feel alarmed by anything in this post. Reality rarely conforms to theoretical human forecasts, which are naturally subject to large errors.

[ronjon]

Latest 00z ECM run now establishes a 1005 mb low pressure in the western Caribbean at 10 days. Something to watch as the the ECM and GFS ensembles hinting at low pressure developing from the CA monsoonal gyre.

[Alyono]

12Z GFS develops a weak tropical storm in the Bahamas this weekend, looks to be heading toward Florida

[Steve]

12Z GFS develops a weak tropical storm in the Bahamas this weekend, looks to be heading toward Florida

Odd track. It forms it on/near the SE FL Coast moving NE and then it loops back around south of Florida into the South Central Gulf and weakens it to a ripple.

[LarryWx]

12Z GFS develops a weak tropical storm in the Bahamas this weekend, looks to be heading toward Florida

Does the UKMET do anything? Although this obviously could just be a phantom, the 12Z CMC has something kind of similar for the same timeframe.