Early Morning thoughts as of 3:30 AM, september 2, 2009.
ERIKA was born officially today with NHC at 4:30 PM this afternoon when they reran the 18 Z model data at 20Z due to the classification. In my personal opinion, if they would have sent recon in on the 31st of Aug , Monday..I think they would have found out that this was a Tropical Depression already. The call for this from the start has been slowly intensifying and basically ERIKA has been behaving quite well in that manner. Perhaps, in some other way she has not, but i will get to that further down in the discussion. As of 2 AM ERIKA was located at 17.0°N 58.7°W...ERIKA went from 50 MPH @ 5 PM to 60 mph @ 8 AM. Since that time ERIKA has become somewhat less organized and I think that could be due to potentially the wind shear that is on the northern side of the system of 20-30 knots.
Looking at the latest guidance...pretty much all guidance tonight with the exception of the 00z NAVY NOGAPS has shifted this to the west. The NOGAPS does ride up along the eastern seaboard but ends up recurving and I think this change comes about because it is actually showing a quite potent ERIKA. All the other guidance from the 00z GGEM, 00z GFDL, 00Z HWRF,00z ECM have shifted to the west. In some cases like the ECM it was quite a considerable shift.
Why the shift? The shift can be explained for quite a few reasons. First off the trough that the GFS and ECM was showing in prior runs..is no longer a valid idea. And to be perfectly honest, with the ECM ensemble means it never was a valid idea. So in the case of the ECM, tonights 00z operational has started to move in the direction of its ensemble in regards to the synoptic setup! The 00z GFS also realized this as well and now has very little weakness in the ridging as it builds it from the Central Atlantic into the NE. This also lies in harmony with the prior consistent runs of the ECM ensemble means. Aside from the ECM ensemble means the only model that was showing this before any other model was the GGEM. The model that HPC labeled as an outlier. The problem is when the GGEM is holding hands with the ECM ensemble means, it quicly becomes more credible.
The GGEM as far as the global models has also been consistently showing a southern solution. Matter of fact as of tonights 00z GGEM it actually takes it over the islands. Current satellite depiction would show that ERIKA is further south then most other global guidance has ERIKA located. Matter of fact ERIKA is getting quite close to the islands considering NHC cone at 5 PM had her spotted pretty much northeast of the islands.
Remember,in the beginning of the discussion I mentioned about her misbehaving in some other way. This would be in regards to the movement of the system. Current 2 AM coordinates were...17.0°N 58.7°W. This is important because 11 PM coordinates were 17.5N 57.6W ..So what this has done is it shows that there was indeed a SW movement with ERIKA which was observed earlier in the evening on the 1st via satellite.
So whats going on here? What is causing ERIKA to move to the SW? Helping factor #1 is the wind shear that ERIKA is experiencing has caused her to weaken. 11 PM pressure was 1004 mbs and 2 AM was 1008. That was a 4 mb rise. Remember a weaker storm will be more prone to follow the lower level steering currents. So lets look at them..
The steering currents actually show why this went SW earlier in the evening and that is because the flow is actually WSW and because of being a weaker system will be more prone to follow that current. So this is the reason in my opinion why she is getting closer to the islands and why she is further SW then 11 PM.
Intensity level once again is going to be the most difficult with this system to forecast. If ERIKA does indeed pass over the islands there is a chance that the land interaction could weaken her more. However, these are relatively small islands, so the effect could be minimal. If it were to pass north of the islands then there would be no effect on ERIKA because of no interaction.
I still think we have to lay three scenarios on the table. Scenario # 1 is to continue to head off to the W or WNW and then eventually NW and potentially make landfall on the east coast.
Scenario #2 is that ERIKA could potentially continue on the WSW and then west tracking and go across the Bahamas and end up going into the GOM, which then depending on whether or not ERIKA can survive the shear and dry air, could become a potential threat somewhere along the USA GOM region. Scenario # 3 which I think needs to be laid out on the table is still the possibility of dissipation. The 00z NAM actually never develops this system and it dissipates.
Out of all the three scenarios that I have laid out...My current thinking is that scenario #1 is the one that has the most potential at this point and time of happening because of the reasons laid out above! So with all the above..I see at this point and time no reason to change my track that was made while ERIKA was an invest and it is at the top of this post. Stay tuned for further updates.
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