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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds. HATE:stagnant weather patterns
  • Location: Taunton, Somerset

    Invest 96W, that formed nearly 2 weeks ago, has finlly been declared a tropical storm, and is located just east of the Philippines. JMA estimate the winds at 35kts. JTWC haven't upgraded the system yet. The precursor to Nakri was a huge monsoon depression with two LLCC's orbiting around each other in a broad cyclonic gyre. The eastern LLCC has lost definition and convection has consolidated near the western LLCC, which is where Nakri's position has been located. Nakri's broad nature, along with some moderate shear, will probably only allow Nakri to strengthen slowly over the next couple of days as it moves towards Taiwan on a northwesterly track.

     

     

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    Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds. HATE:stagnant weather patterns
  • Location: Taunton, Somerset

    Nakri has strengthened slightly, to 40kts according to JMA. JTWC still haven't classified the system. Nakri is a huge system. It's northernmost bands are affecting SW Japan and it's southernmost ones are affecting the Philippines! The system has almost no convection over the very broad LLCC, and the strongest winds and convection are located in the bands. Nakri still resembles a monsoon depression, therefore any further intensification will be slow.

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    Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds. HATE:stagnant weather patterns
  • Location: Taunton, Somerset

    Structurally, Nakri has changed little over the last 24hrs. Winds have increased to 50kts according to JMA, but JTWC still aren't issuing warnings, as Nakri still resembles a monsoon depression, rather than a typical tropical storm. Convection has become much more concentrated in the southern quadrant, but the storm is still extremely broad with a large windfield. Nakri should continue to head north towards South Korea over the next few days. The storm could strengthen  a little more, but because of it's sprawling nature, it probably won't strengthen significantly.

     

    This image shows just how large Nakri is, what an interesting system!

     

    post-1820-0-38866300-1406841766_thumb.jp

     

    Image showing Nakri's bands sprawling from the Philippines right up to Japan (Tropical Storm Halong is located to the southeast:

     

    Posted Image

     

     

     

     

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    Posted
  • Location: The Netherlands
  • Location: The Netherlands

    It is indeed a very impressive and interesting system, especially given its unusual structure. One can say it is remarkable that the JTWC hasn't yet upgraded the system to a tropical storm, given that an ASCAT pass from 13:30 UTC shows winds up to 40 kt to the south of the system:

     

    Posted Image

    ASCAT pass of Nakri (13:30Z, 29-07)

     

    However, there are some points which can argue against designation.

     

    Firstly, the large and broad wind field as noted by Somerset Squall (with peak winds extending to more than 5 degrees latitude below the storm, see ASCAT pass). This coincides with a very elongated wind signature, and the centre appears to be elongated ESE-WNW. (this can be seen by winds changing direction by 180 degrees, located at about 26N, 126E). 

     

    Secondly, the extreme displacement of convection to the south of the centre. This is illustrated by the visible satellite loop below:

     

    Posted Image

    Visible satellite image loop of Nakri (Courtesy: NOAA)

     

    This imagery (as of 22:30 UTC) shows that whatever centre there is (possibly a cyclonic gyre) is located far to the NNW of the convection, an indication that the system is affected by significant northwesterly vertical wind shear. Yet the shear maps are inconclusive about this. Below is a model analysis of the current shear around Nakri:

     

    Posted Image

    Wind shear analysis around Nakri (12Z). The vectors indicate the direction of the shear (often coincident with the upper level flow), while the colours indicate the magnitude of the shear. The centre is located near 26N, 126E (see ASCAT pass). 

     

    Shear analysis indicate there is an upper level anticyclone located overhead, indicated by the wind shear vectors curving anticyclonically outward of the centre of the system. Note that upper level anticyclones are not always located over tropical cyclones.

     

    The anticyclone gives a rather complex shear pattern, with about 35 kt northerly shear to the east and south of the system, and almost no shear near the centre of Nakri. This makes drawing conclusions about the shear pattern near Nakri complicated to say the least.

     

    An interesting fact is that the low level centre elongation axis (which was orientated ESE-WNW, see below ASCAT pass) is directly coincident with the upper level anticyclone elongation axis. Whether and how these mechanisms interplay is unclear to me, but it doesn't appear to be coincidence. Does anybody know if, and if so how these features are interplayed?

     

    But back to the system itself: what also argues against designation is the lack of convection near the centre. This is counteracted by the abundance of convection to the south-southeast. though.

     

    Conclusion

     

    In short: things that argue for designation are the deep and persistent convection to the southeast of Nakri, and the 40 kt sustained winds near the centre. Arguments that are pointing against designation are the broad wind field, the elongated centre and the lack of convection near the centre. Concluding, it is a very difficult and complex situation, with decent arguments for and against designation. Therefore, I'm happy I'm not (yet) a meteorologist  :wink: .

     

    Sources:

    http://www.knmi.nl/scatterometer/ascat_osi_25_prod/ascat_app.cgi

    http://www.usno.navy.mil/JTWC/

    http://www.nrlmry.navy.mil/coamps-web/web/tc?&spg=&sid=96W&ddtg=2014073112

    Edited by Vorticity0123
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    Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds. HATE:stagnant weather patterns
  • Location: Taunton, Somerset

    JMA have upped the winds to 55kts, though these aren't occuring over the centre. This has got to be strongest system JMA have warned on but JTWC haven't.

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    Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds. HATE:stagnant weather patterns
  • Location: Taunton, Somerset

    The broad TS Nakri is closing in on South Korea. The convective mass south of the LLCC has moved into the eastern quadrant of the storm, and is drenching western Japan currently. Nakri, whether it's a true tropical cyclone or not, should weaken soon as it heads over colder water and increased shear, then interacts with land.

     

    Track from JMA (winds are still at 55kts according to this agency, though these winds are not occuring over the largely convectionless centre):

     

    Posted Image

    Edited by Somerset Squall
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    Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds. HATE:stagnant weather patterns
  • Location: Taunton, Somerset

    Nakri has gone through some significant structural changes overnight. Although convection is shallow, it is now peristant over the LLCC, something that has not occured so far with this system. The windfield has contracted also and is more typical of a true tropical cyclone. JTWC have finally started issuing advisories on Nakri for this reason. Nakri is expected to continue to move north towards the west coast of South Korea, where landfall is expected in a couple days.

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    Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds. HATE:stagnant weather patterns
  • Location: Taunton, Somerset

    All the convection associated with Nakri has dissipated, and the circulation is elongating as it approaches the west coast of South Korea. Both JTWC and JMA hve issued their last warnings on the system.

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