ATLANTIC TROPICS ABOUT TO GET BUSY
STARDATE 201909.10 2300 EDT
Now that we had Dorian and an overall increase in overall tropical activity...it seems that any sort of tropical wave activity is going to get a lot of attention especially as we move into the heart of the hurricane season. This has, unfortunately, lead to a lot of speculation which is being enhanced by social media sensationalism which you various see on weather weenie facebook pages.
This sensationalism from these bogus social media pages and accounts are getting into the general public as we are seeing an increase in concerns about whether not tropical disturbance 94L is going to develop. Notice that as system 94L gets weaker and weaker... these same so called weather pages have suddenly stopped talking about 94L or are not pointing out that 94L is getting weaker. And they are not talking about whether not the overall pattern in the tropical Atlantic has become unfavorable for tropical development.
To be fair back I was one of the people that initially thought 94L was going to develop because most of the model data was developing it into a significant system (see my FB page post of
SEPT 6 ) but as we can see the 94L system is collapsing as the overall based state environment in the tropical Atlantic is UNFAVORABLE for tropical development.
Indeed if we take a look at the GFS and the European ensembles for the next 7 to 14 days we see that most of these models actually do show 94L collapsing / dying off. The various LOW pressure areas these models are showing develop in the tropical Atlantic which moves to the northeastern portions of the Caribbean --- all of the red Ls you see on these maps --represent possible tropical systems on ensemble after 144 hours. Given that 94L is already at 45-degree West longitude... there is no possible way that the weather models are picking up 94L and developing it into 6 days from now over the northeast Carribean.
Instead the GFS and the European ensemble models are picking up on the NEXT tropical wave coming off the African Coast (95L) and developing it on D6 and D7 near Puerto Rico and the northeastern portions of the Leeward Islands.
When a meteorologist talks about the overall based state in the Tropical Atlantic ...what we are talking about is the energy at the mid and upper levels the atmosphere. One of the easiest ways to determine this is to use the 200mb ( millibar) Velocity Potential Anomalies or the VPAs. I have talked about this before on the videos so let me briefly go over how these maps work.
Remember that in order to get a tropical storm ...or even a thunderstorm ...or just a regular LOW pressure area ...you have to have a rising UPWARD motion is the atmosphere. The rising vertical upward motion lifts water vapor which condenses and you get cloud formation and precipitation. Likewise SINKING air suppresses precipitation and cloud development.
This image is from September 2. It shows the overall BASE STATE across the entire world. Notice all the Green -which represents strong RISING or UPWARD motion is centered over the western and central portions of the Pacific Ocean. Not surprisingly during the first week of September there were numerous typhoons developing across the central and western Pacific Ocean. However, if you look over in the western hemisphere you will see a strong red and tan colors over North America ...the Caribbean Basin ...and a good portion of the Atlantic as well. This represents a SINKING or DOWNWARD air motion which suppresses tropical development. Now if you notice just east of the Leeward islands conditions were actually neutral ( WHITE) and it was in this area where Dorian began to develop. But for the most part the western hemisphere / the tropical Atlantic on September 2 was in a unfavorable state for tropical development.
This next map however shows the 200mb VPA for the next seven days from September 9 through the 16th.
Notice the intense dark red Tan and orange colors covers all of the tropical Atlantic but in particular over the eastern portions of the tropical Atlantic. This is WHY the overall negative state of the atmosphere in the tropical Atlantic is suppressing tropical systems and it is not a surprise therefore that 94 L is being crushed and is not likely to develop. . Meanwhile in the western and central Pacific Ocean is covered by green and dark green colors which represent rising Motion and enhance favorable areas for tropical development.
However that being said there strong signs that the Atlantic Ocean is about to explode into activity because of a massive change which is going to occur in the above mentioned 200mb velocity potential anomalies.
This image from the European ensemble shows that the pattern in the Atlantic Basin for the next 5 days and it remains quite unfavorable with strong positive 200mb VPA sitting over the tropical Atlantic Ocean. But notice that in the Caribbean Basin and the Southwest Atlantic conditions have moved it to "neutral" (no color).
In the 6-10D the European ensemble shows a major change with strong rising motion ( green/ blue) in the eastern Pacific Ocean off the coast of Mexico and reaching into central America and spreading into the western half Atlantic by September 19.
In the 11 to 15 day we see a huge change in the entire Atlantic Basin which becomes a much more favorable for tropical activity to develop as we move into the heart of the hurricane season.
This a strong supporter by the much improved GFS ensemble mean which also shows strong rising ocean over the central-western portions of the Atlantic and especially in the Caribbean Basin in week two.
And if we look further down the line at the extended European weeklies we can see large areas of green over the entire Atlantic and Caribbean Basin for the next 2 to 4 weeks-- into early October. Again this is a strong signal for the potential of a major increase in activity over the entire Atlantic Basin for tropical storms and hurricanes to develop.
Of course that doesn't mean the activity is going be a threat to eastern US though. In order to know that ...we have to look of the overall pattern. These maps show that the pattern is actually is rather favorable over the next 2-4 weeks to threaten some portion of the U.S..-- IF something were to develop in the tropical Atlantic or the Caribbean.
The various weather models are very insistent on a major trough developing over the Pacific West coast / and southwestern Canada. In response to that ...the atmosphere has to achieve some sort a balance ...so it counters this massive trough over the Western North America by developing an equally strong ridge or heat dome over the Deep South / Delta regions. This forces the jet stream to the north which sets up a warm dry 2nd half of September east of the Mississippi rvier but it also sets a ideal pattern for any tropical storm development to threaten the U.S. East coast or Florida or the Gulf of Mexico.
Indeed looking at the Monday afternoon GFS and European ensembles we see a strong signals for significant tropical Low pressure areas coming out of the Caribbean Basin and moving into the Bahamas on both the GFS and on the European. Both of these models show strong HUGH pressure over the East Coast as the systems approach the Bahamas but whether not the HIGH pressure area stays over the East Coast ( which would protected it) OR if the HIGH moves out into the West Atlantic Ocean which would force the tropical systems into the Southeast US is a question of course we cannot determine at this time