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

METD WEATHER
Akshay Deoras
Severe Weather Forecaster

***UPDATED***

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. 

HERE IS WHAT PEOPLE MUST DO (Via BOM,Australia) 

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.

CATEGORY 1 CYCLONE LEHAR WRAPPING IN DRY AIR?

METD WEATHER
Akshay Deoras
Severe Weather Forecaster,

Today afternoon, Tropical Storm LEHAR intensified to a Category 1 Cyclone as its max sustained winds reached 65 Kt and as of this post continue to be at 65Kt as the cyclone tracked west-northwest at around 07Kt (13km/hr) in the Bay of Bengal about 965km SE of Vizag,1100km east-south east of Machilipatnam,1050km east - south east of Kakinada,Andhra Pradesh and having tracked 200km from Port Blair after bringing heavy rains and winds in the Andaman and Nicobar Islands. However I am personally not convinced with the latest image of the system and some more observations, lets have a look here

Dry Air-

Like mentioned in yesterday's blog post, the amount of dry air entering the Bay of Bengal from East/North East India is increasing every hour as Cyclone LEHAR continues to act like a magnet doing this job. A 24hr comparison of the CIMSS Total Precipitable Water (TPW)clearly shows an increase in the spread of dry air which even now seems to be wrapping around the system in its northern periphery.

The topmost image shows TPW as of yesterday and the below image shows the latest precipitable water. One can see that blue,green region has moved further down (southward) as the Cyclone LEHAR presently at 12.5N,91.0E continues to move NW. Possibly the dry air is interacting with the outer rainbands- Northern and North-Western rainbands of LEHAR as can be possibly inferred from this latest IR-NHC imagery via CIMSS

The 1330UTC obtained NHC enhancement image shows a more or less oval structure of the CDO (Central Dense Overcast) feature which continues to obscure the LLCC. An animation of the IR imagery shows the centre is losing the convergence. It also indicated a possible exposed LLCC (although for a short time) and that the convection is possibly re-organising around a new centre marked by a very favoured wind field as can be seen in this image

The above IR BD image has contours of lower air convergence imposed on it. An increasingly favourable 30Kt region is developing coupled by an excellent poleward flow of 40Kt peak.
SST continues to be very favourable, in the 29C range which is overpowering the moderate 20kt wind shear in the region.

An analysis of all indicates that dry air has likely collided with the outer northern rainbands of Cyclone LEHAR and the convection is re-organising around a new centre and the system is overall maintaining its intensity. Over the next 12hrs, Cyclone LEHAR shall intensify gradually although I don't expect a Rapid Intensification yet considering the fact that wind shear are forecasted to remain moderate all the time in LEHAR's journey. Dry air wrapping shall be a factor to watch out and hence still I don't expect it to intensify beyond Category 2 which shall happen later tomorrow,26th Nov.

Given the fact that dry air interaction will act as a barrier and the SST will be decreasing beyond  36hrs from now ( morning of 27th Nov 2013), LEHAR shall make a landfall as a Category 2 cyclone close to Kakinada,Andhra Pradesh on the morning of Thursday,28th Nov 2013. The state of sea in the Bay of Bengal shall remain ROUGH in this period and hence fishermen shouldn't venture out in the sea till Friday,29th Nov 2013.


More details are awaited like potential damage to Andhra Pradesh coast which will enable to put the graphic map so STAY TUNED!!!

Tropical Storm Lehar approaches Andaman and Nicobar Islands amidst future troubles

METD WEATHER
Akshay Deoras
Severe Weather Forecaster

The newly formed Tropical Storm Lehar is approaching the Andaman and Nicobar Islands now and at the moment passing between Port Blair and Little Andaman Island as can be seen in this IR-NHC image via CIMSS taken at 1330UT,24th Nov.

At the moment, based on DVORAK estimates, Tropical Storm Lehar has peak winds of 55kt i.e about 100km/hr and over the past 6hrs has tracked NW with an increased velocity of 12kt or ~22km/hr (Previously it was tracking by about 15km/hr). Although a CDO (Central Dense Overcast) feature seems to be visible now in the IR-NHC image, Lehar has started running out of trouble as some of its vital parameters at the moment are not supporting it- although it continues to maintain its intensity and has intensified by 10kt in the past few hours.

The primary concern coming now is the sliding drier air from the North (from the mainland of India into Northern Bay of Bengal). Here is a comparison of the latest and pre latest Total Precipitable Water image-

The topmost image shows the Precipitable Water Content- an indicator of the moisture in the atmosphere some hours ago. The area to look for is North of Bay of Bengal where you can see a triangular region of purple,blue,green shades. Now see that region again in the bottommost image. Its very clear that the dry air is sliding down from the mainland into Bay of Bengal and apparently seems to be interacting with the outer rainbands of Tropical Storm Lehar. Dry air is a kind of poison to such thermodynamic systems- Tropical Storm Lehar as it chokes off the thermal engine which leads to weakening of the storm. We are monitoring this region of drier air.. The reason why this dry air is getting pushed south is being discussed. If it slides further south, within 24hrs it will interact with Tropical Storm Lehar and hence the rate of its intensification shall decrease.

The second trouble thats coming up for Lehar is the decreased lower air convergence over the last few hours. Low air convergence is an essential factor for cyclones to intensify. From the past ~25kt low air convergence, the convergence now as per CIMSS stands out to be barely 10-15kt and is offset the CDO/LLCC i.e is SE of the centre of the tropical storm.

IT does appear that over say 12hrs or so the low convergence will be decreasing significantly.
The situation at the upper level is more or less the same. The system had an excellent poleward outflow of 60kt last night which has dropped now to 30kt and the tendency seems to be decreasing ahead as well amidst a moderate wind shear of 20kt...

It does appear that Tropical Storm Lehar won't be intensifying for sometime now, say during the next 12hrs or so. It probably will be disorganise a little given the decreasing convergence. Probably the pressure at the centre which is 996mb shall rise littlebit.

The fate of Tropical Storm Lehar will entirely depend on the above parameters as it churns in a warm sea with present sea surface temperature of 29C. The subtropical ridge (STR) aloft which is steering the system is at the present towards north of the system and over the next 24hrs, the system will be riding under the STR as it becomes parallel to the latitude (non inclined) and after 72hr, the STR shall be south of the system. Unlike Cyclone Phailin, TS Lehar has some factors to non stop affect it (given above ofcourse) and later the cooler sea offshore AP-Odisha coast.

As a result, its being inferred that Tropical Storm Lehar will intensify to A MAXIMUM CATEGORY 2 CYCLONE. This intensification,rather Rapid Intensification shall start after it gets sufficient land clearance,say later tomorrow,25th Nov

Regarding the landfall position, the cone of uncertainty is still high however there are increased chances that the system will land in Andhra Pradesh (South of Vizag) : Near Kakinada on the afternoon of Thursday,28th Nov 2013. Once we have an increased confidence over the landfall area, alert map will be displayed..

Tropical Storm Lehar however shall make a landfall as a Category 2 cyclone (present estimates) with maximum winds of around 175km/hr!

STAY TUNED FOR THE UPDATES 

Tropical Storm "Lehar" threatens India!

METD WEATHER
Akshay Deoras
Severe Weather Forecaster

With just over a month from the landfall of disastrous Category 5 cyclone Phailin  and just a few days after Tropical Storm Helen , the Bay of Bengal is all set to host another Tropical Cyclone which will be soon officially called as "Cyclone Lehar".. At METD WEATHER, Saffir Simpson Scale is followed and hence we have already named the area of deeply organised convection about 1560km SE of Vizag,Andhra Pradesh as Tropical Storm Lehar given the estimated maximum sustained winds of 35kt as of today morning. This Tropical Storm which at present lies in the periphery of land, The Andaman and Nicobar Islands is all set to pass dangerously between Little Andaman Island and Port Blair between late tonight, 24th Nov and morning of tomorrow,25th Nov 2013 as a "Tropical Storm category" with max winds reaching upto 100Km/hr accompanied by strong rains and storm surge likely upto 10ft.... Lets have a look at the dynamics of Tropical Storm Lehar in the Bay of Bengal-

Shown above is a composite view of Tropical Storm Lehar. The topmost simple Infrared view (top left) and IR-BD view (Top Right) clearly shows almost circular convection centre with cloud tops reaching upto -70C which is an indicator of organising convection and intensification of the system. Interesting thing to note in the lower images is the organising of outer bands- rain bands- banding feature around the LLCC (Low level circular centre) as can be inferred in the NRL images. The lack of symmetry is being attributed to the periphery of the land which isn't allowing the system to undergo rapid intensification stage as it churns in the sea having temperature of 29C...

A look at the wind profiles & dynamics show that Tropical Storm Lehar is being troubled by moderate wind shear of 30kt to the north and south of the centre and 20kt to its East disabling it to intensify robustly. Over the past 12hrs, convergence at the lower atmospheric profile has decreased slightly along with the poleward outflow which now stands to be 40kt peak as against 60kt peak 12hrs ago...

As the system steers North West slowly ( at present with a velocity of 17km/hr), after the encounter with Andaman and Nicobar Islands, the system shall get a clearance from land to intensify.

Shown above is the Sea Surface Temperature view via CIMSS.. Here Red colour represents Sea Surface Temperature of 30C, Orange shows 29C, yellow shows 27-28C. Thus the sea coupled with the moisture content will be favourable for intensification. But the question arises, will Tropical Storm Lehar reach a Category 5 status like Tropical Cyclone Phailin ??

The answer at the moment seems- NO

Here is the reason,

This is CIMSS view of the wind shear in knots across Bay of Bengal.. Here solid white lines indicate an increasing shear tendency: unfavourable for storm intensification. Over the Bay of Bengal, it seems the wind shears will remain considerably higher than they were during Phailin's time as a result this factor will always try to reduce the intensity but with other factors favourable, Tropical Storm Lehar shall intensify to atleast Category 2 although JTWC says it can go upto Category 3. As the sea few hundred kilometers offshore Odisha and Andhra Pradesh is slightly cooler, intensification may not be that high and hence for now, people shouldn't panic or compare this cyclone with Phailin or Supercyclone of 1999 or with the US hurricane like Katrina.

Where will it head ?

This is always a million dollar question. At the moment, the sub tropical ridge seems to be steering the system towards Indian coast but the area in North Bay of Bengal is being monitored for the development of high pressure at the lower levels (850mb or say 5000 ft AGL). If the high pressure forms in that region, the cyclone shall not move much North in its NW journey and in that case its region of landfall shall be south of Vizag in Andhra Pradesh on the morning of 28th Nov 2013, Thursday.. 

However as GFS 00z is showing, if the high pressure doesn't form, system under the influence of sub-tropical jet stream of India will curve a bit north and make a landfall near Brahmapur,Odisha- apparently at the same place like Cyclone Phailin on the morning of 28th Nov 2013, Thursday

Where ever it shall head, people living along the coastal line from Kakinada,AP till Brahmapur,Odisha shall pay attention towards the development of this system which will be covered on METD WEATHER's facebook page (www.facebook.com/deorasakshay) and on this blog also

Once the forecast becomes more clear, an alert map will be issued by METD WEATHER

*** Preparation*** 

Rough Sea of Bay of Bengal will start now onwards and will continue till Thursday,28th Nov. Fisherman are requested not to venture with their ships/boats.. 

VIA BOM,Australia (People of Andhra Pradesh-Odisha Coast must note) 

When a cyclone watch is issued

• Re-check your property for any loose material and tie down (or fill with water) all large, relatively light items such as boats and rubbish bins.
• Fill vehicles' fuel tanks. Check your emergency kit and fill water containers.
• Ensure household members know which is the strongest part of the house and what to do in the event of a cyclone warning or an evacuation.
• Tune to your local radio/TV for further information and warnings.
• Check that neighbours are aware of the situation and are preparing.