Invest 94L and the Conditions and Steering Pattern in the Atlantic Basin

By: GTstormChaserCaleb , 2:07 AM GMT on August 11, 2014

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Hi and Good Evening, today I will talk about Invest 94L in the far eastern Atlantic and the conditions and steering pattern in front of it.

94L is currently in a moist environment embedded within the monsoon trough or ITCZ whichever one you prefer to call it.


Fig. 1 Tropical Atlantic Surface Analysis as of the 18 UTC advisory of the 10th day of August 2014.


As of the latest Tropical Weather Outlook (TWO) the National Hurricane Center (NHC) states that 94L has acquired a broad area of low pressure and has given it a 10% chance to develop within the next 2 days and a 40% chance to develop thereafter. I'm going with a 50% chance of this ever developing.


94L will be moving into an environment in front of it where the airmass is dry and stable which is a result of the SAL and a strong Azores High. This has resulted in low vertical instability. Tropical Cyclones need rising air and convergence to develop and when that air is sinking thunderstorms that try to grow with height collapse. This was the case with TD 2 and Hurricane Bertha in her premature stage.

Current Relative Humidity or RH Levels show dry air up at about 250-500 mb. right in front of 94L extending to 28 W and perhaps further west to about 42 W.


Fig. 2 GFS depiction of the Vertical Cross Section of 94L as of the 18 UTC model run.
(Courtesy of Levi Cowan)


The tropical wave that is currently over the Windward Islands helped to moisten the environment from about 42 W to 61 W, where the south axis of the wave sits and is generating showers and thunderstorms this evening. So 94L will have some work to do to clear through the SAL and mid level dry air in front of it. At least currently it has a solid field of moisture embedded within the monsoon trough and a stretched out 850 mb. vorticity. to work with. The monsoon trough will continue to feed moisture into 94L, but will also retard development since it is such a broad low. As soon as it pulls away from the monsoon trough however it will be all on its own and be able to consolidate further. Since TD 2 and Hurricane Bertha had similar conditions to fight through I think 94L will survive the trek across the Central Atlantic where as it nears the Lesser Antilles should began to organize even further similar to Bertha.

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Fig. 3 Shows the extent of SAL in the Atlantic as well as the mid-upper level dry air.


Due to the persistent and progressive troughs along the East Coast of the US the western flank of the A-B High is rather weak and as a result the trade winds have relaxed.


Fig 4. Water Vapor Satellite loop of the Tropical Atlantic shows the Tropical Wave approaching the islands and slowing down.


Now to some steering. I have been looking at a blend of the CFS and GFS 500 mb. heights out to 2 weeks or at 360 hrs. and I have been noticing an anomalous ridging pattern wanting to set up over the Atlantic and extending into the CONUS during that time with nearly no troughing or at least not as pronounced of a troughing pattern we have seen the past few weeks along the East Coast of the US which was responsible for recurving Bertha away from the US and bringing flooding to parts of North Carolina. Instead, the GFS shows a bubble of High Pressure developing over the Northeast. The Subtropical Ridge seems to want to nose in and bridge with the CONUS Ridge. If you look at figure 5 below notice the 588 dm. line extends all the way to Arizona.


Fig. 5 CFS 500 mb. heights for the North Atlantic as of the 0 UTC model run.
(Courtesy of Levi Cowan)


Fig. 6 GFS 500 mb. heights for the North Atlantic as of the 0 UTC model run
(Courtesy of Levi Cowan)


So what does this mean for 94L? Well it means that 94L should take a more westerly path into the Caribbean and continue on that same general heading all the way towards the Yucatan and ultimately end up in the BOC. Now the itching question on everyone's mind is can 94L make it into the GOM? And to answer that it certainly can if the system can get strong enough and find a weakness in the ridge. In fact, in figure 7 below some of the GFS ensemble members portray that scenario happening.


Fig. 7 GFS Ensemble Members Mean Sea Level Pressure (MSLP) and Normalized Anomaly


And this is where things get interesting if upper level conditions in the Caribbean allow for strengthening meaning westerly winds decrease enough where wind shear doesn't become a problem and the TUTT pulls away or lifts north of the Bahamas, then 94L may find its way to some of the warmest waters in the entire Atlantic Basin which is in the Western Caribbean, and over the highest TCHP content where at that time it will have the potential to strengthen even further and perhaps undergo rapid intensification.


Fig. 8 Current Sea Surface Temperatures across the Atlantic Basin
(Courtesy of Levi Cowan)


Fig. 9 Tropical Cyclone Heat Potential (TCHP)


However, before it can even get there it must pass through an area in the Atlantic which has become a death zone for tropical cyclone development known as the MDR. If it can get through the stable airmass and cut through the SAL without being reduced to dust then it will have an ample opportunity to organize a lot closer to the islands and this is where that dangerous pattern comes into play. So interests in the Lesser Antilles should keep an eye on 94L and monitor your local weather agencies for updates on this potential storm.

Thank you all for reading and have a good night.



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5. VR46L
8:31 PM GMT on August 11, 2014

Hiya Caleb ...

The Gulf is setting up to be ROCKET FUEL soon :)

One thing I will say about this year The dust is Nowhere near as bad as last !
Member Since: March 1, 2012 Posts: 0 Comments: 6927
4. Astrometeor
8:03 PM GMT on August 11, 2014
Good blog, btw.
Member Since: July 2, 2012 Posts: 101 Comments: 10344
3. Astrometeor
8:02 PM GMT on August 11, 2014
Good thing you weren't Kori earlier. I was brutally attacking him for his lame forecasting skills.
Member Since: July 2, 2012 Posts: 101 Comments: 10344
2. Doppler22
7:58 PM GMT on August 11, 2014
BORING. I fell asleep and ug. XD XD XD XD JUST KIDDING!!!! Great entry Caleb and thanks for the analysis. It will be interesting to see this thing evolve, and hopefully it does so before I get my new job so I can track it :p
Member Since: February 13, 2012 Posts: 11 Comments: 3779
1. AtHomeInTX
2:48 AM GMT on August 11, 2014
Thanks Caleb. Great analysis.
Member Since: August 24, 2010 Posts: 0 Comments: 245

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