Wednesday, November 27, 2013

"Cyclone Lehar" ingests dry air, weakens as per the expectation

Akshay Deoras
Severe Weather Forecaster


0928am IST,28th Nov 2013- Former Cyclone Lehar weakens to a Tropical Depression and shall be striking AP as a weak Tropical Depression........ 

It turned out to be a a very major day for Cyclone Lehar as it behaved completely against the forecasts...however obeyed METD WEATHER's forecast. The dry air which it pulled from Eastern India finally started showing its effect from yesterday night as it put a lid on the intensity of the cyclone. Cyclone Lehar's central core became very unstable since last night which continued till today afternoon where the CDO (Central Dense Overcast) feature vanished which allowed the LLCC (Low Level Circulation Centre) to appear in some of the IR satellite images obtained today morning. As of now, we are waiting for JTWC update on the max winds of Cyclone Lehar which shall be a Tropical Storm Lehar now given the fact that its maximum sustained winds should be on the borderline of Tropical Storm and Category 1 as per the Saffir Simpson Scale where from 64kt onwards (119km/hr), systems are rated as Category 1 and below that till 35kt (63km/hr), the system is a Tropical Storm...

Lets have a look at how dry air killed/chocked the system: Category 1 Cyclone LEHAR

Above image is the CIMSS TPW (Total Precipitable Water) image of yesterday which clearly shows how much the dry air had increased around the western quadrant of Cyclone Lehar. Due to some reasons, this dry air wasn't entering the circulation centre which actually is the thermal engine driving the entire system.

Above is the IR NHC image of yesterday morning which showed how stable the centre was in comparison with the below image of today afternoon when the system started showing first signs of weakening on rapid scale. Below image clearly shows a rapid warming of the central core- a typical indicator of increasing cloud top temperature (Present peak cloud top temperature is about -40/-50C as against -70/-80C which was today morning/yesterday)... Dry air ingestion does such thing causing temperature inversion which ultimately inhibtis the growth of CB clouds and weakens the system.

Below is the latest IR NHC CIMSS image of supposed Tropical Storm Lehar as CIMSS is showing. Now comparing the above and below image, one can infer how rapidly the system is disintegrating..

Dry air ingestion/wrapping around the system can be seen from this latest TPW image. Notice how the dry air is wrapping around most of the system and its thermal content has decreased (has become less shaded brown)... In the coming period, dry air will wrap more, ingest more and practically it will completely disintegrate the system

So what will happen now? 

As a Tropical Storm, Lehar will hit Andhra Pradesh coast around Machilipatnam tomorrow,28th Nov 2013 morning period- stretching to afternoon also. Given the disintegration rate, it seems Lehar will hit the coast at a max sustained winds of 45-50kt around 90km/hr... gusting to around 100km/hr or so.. The landfall zone shall stretch between Machilipatnam and Kalipatnam (AP) 

Heavy rains will be witnessed in these areas and probably the storm surge will be around 3-4feet. 


When a cyclone warning is issued (For Andhra Pradesh coastal areas) 

Depending on official advice provided by your local authorities as the event evolves; the following actions may be warranted.
  • If requested by local authorities, collect children from school or childcare centre and go home.
  • Park vehicles under solid shelter (hand brake on and in gear).
  • Put wooden or plastic outdoor furniture in your pool or inside with other loose items.
  • Close shutters or board-up or heavily tape all windows. Draw curtains and lock doors.
  • Pack an evacuation kit of warm clothes, essential medications, baby formula, nappies,
    valuables, important papers, photos and mementos in waterproof bags to be taken with
    your emergency kit. Large/heavy valuables could be protected in a strong cupboard.
  • Remain indoors (with your pets). Stay tuned to your local radio/TV for further information.

On warning of local evacuation (Near landfall area, around Machilipatnam)

Based on predicted wind speeds and storm surge heights, evacuation may be necessary.
Official advice will be given on local radio/TV regarding safe routes and when to move.
  • Wear strong shoes (not thongs) and tough clothing for protection.
  • Lock doors; turn off power, gas, and water; take your evacuation and emergency kits.
  • If evacuating inland (out of town), take pets and leave early to avoid heavy traffic, flooding and wind hazards.
  • If evacuating to a public shelter or higher location, follow police and State/Territory Emergency Services directions.
  • If going to a public shelter, take bedding needs and books or games for children.
  • Leave pets protected and with food and water.

When the cyclone strikes 

  • Disconnect all electrical appliances. Listen to your battery radio for updates.
  • Stay inside and shelter {well clear of windows) in the strongest part of the building,
    i.e. cellar, internal hallway or bathroom. Keep evacuation and emergency kits with you.
  • If the building starts to break up, protect yourself with mattresses, rugs or blankets under a
    strong table or bench or hold onto a solid fixture, e.g. a water pipe.
  • Beware the calm 'eye'. If the wind drops, don't assume the cyclone is over; violent winds
    will soon resume from another direction. Wait for the official 'all clear'.
  • If driving, stop (handbrake on and in gear) - but well away from the sea and clear of trees,
    power lines and streams. Stay in the vehicle.

After the cyclone

  • Don't go outside until officially advised it is safe.
  • Check for gas leaks. Don't use electric appliances if wet.
  • Listen to local radio for official warnings and advice.
  • If you have to evacuate, or did so earlier, don't return until advised. Use a recommended route and don't rush.
  • Beware of damaged power lines, bridges, buildings, trees, and don't enter floodwaters.
  • Heed all warnings and don't go sightseeing. Check/help neighbours instead.
  • Don't make unnecessary telephone calls.
Note: Managers of resorts, hotels, motels, and caravan parks should take steps to ensure visitors are aware of the dangers and know what to do in the event of a cyclone. Free Protecting Caravans information is available from your State/Territory Emergency Service.

1 comment:

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