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    • By Spawney
      Strange looking orange sun due to the Saharan dust and smoke from the Spanish/Portuguese wildfires blown over by Ophelia.
    • By zaax
      The national weather forcast said Ophelia might hit us next week. Any comments?
       
      http://www.nhc.noaa.gov/graphics_at2.shtml?cone#contents
    • By Vorticity0123
      Well, what a record-breaking day it has been in the Eastern and Central Pacific it has been today! As of speaking, three (3!) major hurricanes are roaming the Pacific waters at the same time, which is unpreceded in these areas. It is likely that this activity has been aided by the ongoing El Nino event, which has caused anomalously warm waters in the Central and Eastern Pacific. In this post I will provide some details about the cyclones individually, as well as a short look into the causes of this record-breaking activity.
       
      A sight to behold
       
      Below is an impressive satellite image showing all three systems in daylight:
       

      Satellite image of (from left to right) Kilo, Ignacio and Jimena. Courtesy: NOAA.
       
      All three systems show up clearly as well-organized hurricanes with an eye visible surrounded by intense convection.
       
      Kilo: a very stubborn cyclone
       
      The leftmost one, and probably also the one with the most interesting history, is hurricane Kilo. Just 24 hours ago, the system was still a 60-knot tropical storm, and now it has almost doubled its intensity up to 110 kt. Exactly what one could call rapid intensification. This make the system a category 3 hurricane on the Saffir Simpson Hurricane Scale.
       
      However, the most remarkable thing is that this system has been more noteworthy for its lack of intensification so far. During the past several days, Kilo was continuously forecast to become a hurricane, which it refuse to do, up to now. It stubbornly stayed as a tropical depression in seemingly favourable environment.
       
      Furthermore, its track has also defied forecasts quite a few times (also partly because it stayed so weak), as also alluded to by Somerset Squall in the thread about this cyclone. Originally, Kilo was forecast to strike Hawaii as a hurricane a week ago as well. Fortunately, this was not the case. Here's a link to the appropriate thread.
       
      https://forum.netweather.tv/topic/83810-hurricane-kilo/
       
      Ignacio to possibly threaten Hawaii
       
      The center one is hurricane Ignacio. This cyclone developed in the Eastern Pacific and crossed 140 degrees longitude into the Central Pacific. Initially refusing to intensify quickly as a category 1 hurricane, Ignacio also put up a burst of rapid intensification. As of writing, the cyclone is now a category 4 hurricane with 120 knot winds.
       
      What is noteworthy about Ignacio is that it may be a threat for Hawaii in a few days, as it moves closer to the islands from the southwest. Currently, the CPHC forecasts the cyclone to pass safely to the north of the islands, only causing high surf among the islands.
       
      Another unusual thing about the forecast of Ignacio is that it is anticipated to stay a hurricane while passing north of the islands. Cyclones like Ignacio seldom retain hurricane intensity while passing to the north of the Hawaiian islands from the east.
       
      More to be found here:
       
      https://forum.netweather.tv/topic/83855-major-hurricane-ignacio/
       
      Jimena to undergo eyewall replacement cycle
       
      Finally, the easternmost cyclone that can be seen here is Jimena. As of speaking, Jimena has already past her peak, and is now a 120 knot system, making it a category 4 hurricane. Her intial peak was reached 6 hours ago at 130 knots. Talking about rapid intensification, Jimena managed to get from 25 kt to 130 kt in merely 3 days!
       
      The NHC has noted that Jimena has developed concentric eyewalls, which means it is likely to embark onto an eyewall replacement cycle. In such a cycle, the inner eyewall weakens and dissipates, while a new, larger outer eyewall becomes better defined. In this process, the eye becomes much larger and the system itself usually weakens a bit. After completing such a cycle, a new round of intesification can begin assuming that favourable environmental conditions prevail. This could also be the case for Jimena. So far, the system is not forecast to hit land.
       
      Here is her own topic: https://forum.netweather.tv/topic/83870-major-hurricane-jimena/
       
      Anomalously warm waters due to El Nino
       
      One of the major causes of this unique event appears to be related to the El Nino that is currently active. Below is a map of the SST (sea surface temperature) anomalies of the 27th of August:
       

      SST anomalies as of 27 August. Courtesy: NOAA.
       
      For clarity, the black box roughly indicates the area in which the tropical cyclones are residing. Note that this area does not explicitly overlap with the most significant warm waters near the Equator associated with the El Nino event. Still, sea surface temperatures inthe encircled area are much warmer than average, contributing in the increased tropical activity.
       
      Summary
       
      An impressive event to say the least, three consecutive major hurricanes active in the Eastern and Central Pacific. Possibly we will even be facing one or two category five hurricanes in the very near future. Much more can be said about these systems, so do not hesitate to add any facts/statistics/any other things you might think of .
       
      Finally, just because of the amazing sight, below is a loop of the three tropical cyclones at major hurricane intensity. Click to activate.
       

      Satellite loop of the Eastern and Central Pacific. Click to activate. Courtesy: NOAA.
       
      Sources:
      http://www.nhc.noaa.gov/satellite.php
      http://www.nhc.noaa.gov/
      http://www.prh.noaa.gov/cphc/tcpages/archive.php
      http://www.ospo.noaa.gov/Products/ocean/sst/anomaly/
       
    • By Thunderbolt_
      Mediterranean tropical cyclones, known as "medicanes", are a rare meteorological phenomenon in which tropical cyclones form in the Mediterranean Sea. The reason why they are so rare is because the Mediterranean region is fairly dry and so tropical cyclongenesis cannot occur, however if moisture is able to reach the region, usually in the form of a extratropical cyclone from the North Atlantic, then it may pass over the warmer waters of the sea and undergo tropical transition into a tropical cyclone.
       
      They are more common in the autumn and winter months when the jetstream moves farther south and allows low-pressure areas to reach the Mediterranean region.
       
      There have been rare instances of them though. Between 1948 and 2011, only 99 low-pressure systems with tropical or subtropical characteristics formed in the Mediterranean Basin. One example is the storm pictured below that formed in January 1995, that formed a distinctive eye.

    • By Vorticity0123
      After a lull of about a month in TC activity, a new subtropical storm has developed in the Central Atlantic, and it has been named Melissa. The system is quite large, and seems to have a quite large range of tropical storm winds, but in the last few hours, convection has also built at the center of Melissa, which is a characteristic of a (sub-)tropical cyclone.
      Current OSCAT data shows the large radius of tropical storm winds associated with the system (winds of at least three and a half flag suggest tropical storm force winds)

       
      Current water vapor imagery shows a tongue of dry air curving toward the center of Melissa, likely impeding in development.
       

       
      Shear analysis by CIMSS (not shown here) shows the system is currently in a sharp shear gradient, with values ranging from 20 kt to the east, to 50 kt to the west of the system, providing, along with the dry air, only marginal conditions for development.
       
      The NHC is currently forecasting Melissa to get close to hurricane strength, as shear values are expected to drop to values below 10 kt, and SSTS are about 27 degrees Celsius. Thereafter, extratropical transition is about to begin.
       
      The storm is forecast to move northward during most of its lifetime, with a recurve toward the northeast afterward. Behind that time, it is yet uncertain if the system will turn back toward Greenland, or continue its recurve toward Spain. The NHC is currently forecasting a backward curve toward Greenland, on which an increasing amount of models seem to agree upon.
       

      The track of Melissa as forecast by the NHC.
       
      Although the model spread has been reduced in the past 24 hours, there remains a considerable amount of uncertanity about the angle of the recurve.
       

       
      An image of the different forecasts of different models, showing the current spread at the medium to long range.
       
      It will be interesting to see how the models handle this system now it has been qualified as a subtropical storm, and especially the effects on the forecasted blockade west of Ireland. It is likely that there will be quite some model-hopping in the medium to long term time frame. It is also very nice to see how tropical cyclones could have a significant impact on the weather in Europe, directly or indirectly.
       
      To illustrate the model-hopping of the various models on the handling on the storm, some output of the GFS and ECMWF models at T96hr below:
       
      GFS:

      EC:

       
      While the GFS suggests a very pronounced southern part of the complex low pressure area (extreme left, remnants of Melissa), the ECMWF shows a much more pronounced northern part of the system (in this case, the remnants of Melissa would be absorbed). The different handle could easily result in very different outcomes at bigger timeframes.
       
      And finally (to get back to the storm itself), a visible image of the subtropical cyclone.

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