Thu Jul 27 2017 12:22 PM

An active portion of the monsoon trof located in the east-central Tropical Atlantic and associated with a tropical wave has been showing some signs of developing one or two areas of low pressure that models increasingly suggest will interact with an additional wave, or waves plural, coming off of Africa later this week and/or next. Another consideration is an expected positive phase of both the MJO and CCKW crossing the Atlantic as we head into August.

Environmental conditions are already marginally favorable for development, and looked at from 50,000', this highlighted region is likely to become somewhat more favorable for tropical cyclone formation over the next three to ten days, and NHC does give it a 30% chance of development into a tropical cyclone within the next five (by early August), which could be conservative.

Quoting from this morning's TWD

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
652 AM EDT Thu Jul 27 2017

Based on 0600 UTC surface analysis and satellite imagery through 1015 UTC.


An eastern Atlantic tropical wave has its axis along 30W from 04N
to 17N, moving westward at an estimated 24 hour motion of about
10 kt. First visible METEOSAT images show what appears to be a
low to mid-level cyclonic circulation just west of the wave near
11N31W. Satellite images from during the overnight hours showed
and are still showing increasing convection over and near this
circulation. The convection is of the scattered moderate intensity
just north of where the wave crosses the monsoon trough from
11N-12N between 29W-31W. However, the METEOSAT-9 imagery shows
abundant dense Saharan dry air and dust across the wave north of
13N. Isolated showers and thunderstorms are elsewhere within 120
nm either side of the wave south of 13N.

July 30 Update
Early on July 28 this feature was tagged with an invest number, 97L, and the title of this Lounge thread was updated accordingly. However, that particular wave interaction fell apart, but as expected by some model runs, two new waves are now starting to interact and dominate, and slow development within this broad area of low pressure is becoming possible again during the new week.

August 3 Update
The more convectively active pocket of the Monsoon Trof has been dragged into the Caribbean with one of the expected waves, and some models are starting to sniff out development from this feature should it track into the Gulf of Mexico. This is now definitely something to watch over the weekend and into next week. The next Invest tag to be used here would be 90L

August 3rd 2 PM Update
As of the Aug 03 2PM NHC TWO, this disturbance is now being tracked as Invest 90L and the title has been updated accordingly.

August 6th 3:30 PM Update
Invest 90L is now being referred to as SEVEN and the title has been updated accordingly.

August 6th 10:45 PM Update
Ptnl SEVEN has become Tropical Storm Franklin.
- Ciel

This is where to put mid to long range thoughts on this feature's potential for development, intensity, and forecast track. Longer range model output discussions are appropriate here.

Fri Jul 28 2017 10:53 AM
Re: 97L Lounge

While the two low to mid level circulations located within this broad area of low pressure have sustained, inhibitive influences of large scale atmospheric waves are likely to keep development in check for at least another 24 to 72 hours, and unsurprisingly, NHC 5 day odds have actually dropped back down to 20% as of this morning, July 28.

By the middle of next week, the environment in the central to eastern Atlantic is still forecast to be somewhat favorable for development, while at the same time an additional wave is likely to converge with this feature. Lots of time to watch out here.

Thu Aug 03 2017 11:10 AM
Re: Caribbean Wave

The convectively active pocket of the Monsoon Trof we have been watching over the past week has merged with a significant tropical wave and has been dragged into the eastern Caribbean. This area of disturbed weather is looking unusually frisky, considering its location - the eastern Caribbean. Conditions for development are actually marginally favorable already, and look to become more so as the disturbance continues west to west-northwest. The NHC will likely highlight this feature today.

(Weather Analyst)
Thu Aug 03 2017 02:18 PM
Re: Caribbean Wave

NRL now showing this as invest 90L

Thu Aug 03 2017 07:56 PM
Re: Caribbean Wave


The 18z GFS does not really develop this system (90L) but it also keeps it close to the Mexican coastline along the south.

However the 12Z Euro starts to develop it before a Yucatan landfall on Tuesday, then develops it into a hurricane in the Bay of Campeche and it makes landfall in Mexico next Thursday. just north of Tampico.

Fri Aug 04 2017 06:18 AM
Re: Caribbean Wave

The 0z GFS brings this system into Mexico near the south end of the Bay of Campeche, as a tropical storm The 0z Euro continues to show a hurricane hitting just north of Tampico. Very little change from the prior runs for 90L.

The 6z GFS is a bit stronger, possibly hurricane, and takes it in near Tampico, Mexico on Friday August 11th.

(Weather Guru)
Fri Aug 04 2017 07:14 AM
Re: Caribbean Wave

The Navgem agrees with the GFS, although it has it much stronger.

Sat Aug 05 2017 12:08 PM
Re: Caribbean Wave

Today's 12Z GFS develops it in the south BOC and moves it in a strong TS or hurricane in the southern east coast of Mexico in the BOC Thursday morning. It may develop a bit before landfall in the Yucatan also, but not much.

Recon is scheduled to fly out there tomorrow. Of the two systems 90 and 99L, this one (90L) is more likely to develop.

Sat Aug 05 2017 02:24 PM
Re: Caribbean Wave

12Z Euro starts to ramp up the system once it gets into the Gulf of Honduras, when it makes landfall on the Yucatan it is ramping up, after getting in the bay of campeche it rapidly strengthens and makes landfall near Tampico Thursday as a hurricane.

Sun Aug 06 2017 02:07 PM
Re: Caribbean Wave

The 12Z GFS shows this developing in about 24 hours, but current conditions could have it develop a lot sooner, then landfall near Mahahual Mexico on late Monday into Tuesday as a Tropical storm or Hurricane. Exits back into the bay of Campeche on tuesday night. Landfall south of Tampico as a hurricane on Thursday morning.

12z euro develops it tonight or tomorrow morning, with landfall similar to GFS on the Yucatan Monday night.

Sun Aug 06 2017 03:52 PM
Re: Invest SEVEN Lounge

Invest 90L is now SEVEN

Conditions ahead for SEVEN are very conducive for development, and possibly rapid at times. Shear is quite low, and SSTs high. A formidable hurricane into initial landfall is a distinct possibility, with an equal or greater chance that SEVEN becomes a hurricane (for the first time, or again) should it reappear in the Bay of Campeche/S Gulf of Mexico.

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