Dangerous Cyclone Mahasen gathering strength in the Bay of Bengal

By: Dr. Jeff Masters , 4:25 PM GMT on May 11, 2013

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Dangerous Tropical Cyclone Mahasen is gathering strength over the Indian Ocean's Bay of Bengal, and is a potential major threat to Bangladesh and Myanmar. The 11 am EDT Saturday advisory from the Joint Typhoon Warning Center put Mahasen's top sustained winds at 55 mph, with a motion northwest at 19 mph into the center of the Bay of Bengal. Satellite loops show that Mahasen has a large area of intense thunderstorms with very cold cloud tops that reach high into the atmosphere. The cloud pattern is not well-organized, with little spiral banding. However, the cyclone has developed respectable upper-level outflow channels to the north and east, which are ventilating the storm by carrying away air converging to the center near the surface. High wind shear of 20 - 25 knots is affecting the storm, which is keeping the system disorganized. However, wind shear has declined about 5 knots since Friday, and is predicted to fall to the moderate range, 10 - 20 knots, by Sunday. This should allow organization into a Category 1 storm on Sunday. Aiding this process will be Mahasen's motion away from the Equator, which will help the cyclone leverage the Earth's spin to get itself spinning faster. Also aiding the intensification process will be ocean waters that are an exceptionally warm 31°C (88°F). This is about 1°C warmer than average for this time of year.


Figure 1. Latest satellite image of Tropical Cyclone Mahasen gathering strength over the Indian Ocean's Bay of Bengal.

Forecast for Mahasen
The official forecast brings Mahasen to Category 1 strength before landfall occurs in Bangladesh near the Myanmar border on Wednesday. Comparative model forecasts of Mahasen from the GFS, ECMWF, UKMET, GEM, NAVGEM, and FIM models show wide disagreement on the future intensity and speed of the storm, though. It is possible that wind shear will keep the storm disorganized and below hurricane strength until landfall, as suggested by the GFS and ECMWF models. The 06 UTC forecast from the HWRF model brings Mahasen to Category 3 strength on Monday, but weakens the storm to tropical storm strength at landfall. The model predicts that the storm will dump a significant area of heavy rains of 32 cm (12.6") over Maynmar and Bangladesh. The storm surge, high winds, and heavy rains of Mahasen are a huge concern for the thousands of Myanmar refugees living near the coast in makeshift camps, as reported by the New York Times.


Figure 2. Double trouble: Tropical Cyclone Jamala (lower) and Tropical Cyclone Mahasen (upper storm) spin on opposite sides of the Equator in this in this MODIS image taken at 04:25 UTC May 10, 2013. Mahasen is the name of a King of Sri Lanka from the 3rd century. Image credit: NASA.

MJO pulse that spawned Mahasen headed towards the Atlantic
Mahasen spun up in response to an active phase of the Madden Julian Oscillation (MJO) that has been moving through the Indian Ocean during the past week. The MJO is a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days. The strong MJO pulse coincided with a convectively coupled atmospheric Kelvin wave (CCKW), a wave of increased heat and moisture propagating along the Equator, which helped increase thunderstorm activity. The active pulse of the Madden Julian Oscillation is expected to reach the Western Caribbean sometime May 22 - 26, and there will be a heightened chance of an early-season tropical storm forming in the Eastern Pacific and Western Caribbean during that time period.

There is a small disturbance a few hundred miles north of Puerto Rico today that has developed some spin and a bit of heavy thunderstorm activity. This system is over cool waters of 77 - 79°F, and will likely be torn apart by high wind shear on Sunday.

Resources
Comparative model forecasts of Mahasen from the GFS, ECMWF, UKMET, GEM, NAVGEM, and FIM models

India Meteorological Department's tropical cyclone page

Bangladesh Meteorological Department Warning

Myanmar Dept. of Meteorology and Hydrology Warning

Tutorial on Equatorial Waves in the COMET program's Introduction to Tropical Meteorology, plus their case exercise built around the May 2002 "twin twins" case, for use in a tropical synoptic course.

Jeff Masters

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997mb over Cuba on the 18z. The incipient disturbance is now showing up on the 0-192hr high-res portion of the GFS run.

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372


384
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Member Since: June 20, 2012 Posts: 0 Comments: 2159
18z GFS at 360 hours:

Member Since: July 21, 2011 Posts: 83 Comments: 7167
Quoting Levi32:


He said once that he uses 400mb because the tropopause is higher in the tropics.
That makes sense. I still think 500mbs offers a better or "truer" view of the mid-level, however.
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348


360
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GFS continues to forecast wet activity across much of the western Caribbean and a possibility of a tropical cyclone development.

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300 hours
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252 hours
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Member Since: July 21, 2011 Posts: 83 Comments: 7167
nighty night little AOI



Member Since: July 15, 2006 Posts: 174 Comments: 54353
Low level center is now in the nude. Commence system deterioration.

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pretty cool monday morning coming up
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Quoting TomTaylor:
I was always confused by Bastardi's use of non-standard atmospheric levels, particularly 600mb and 400mb. Why not just use 500mb? Basically same thing.

Think I figured out why he does this though and it's because UAH AMSU global temperature traces in the mid-troposphere are only available at 400 and 600mbs. LinkIndeed


He said once that he uses 400mb because the tropopause is higher in the tropics.
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Humidity is NICE...
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Normal (KRAL) 80 °F 55 °F
Record (KRAL) 104 °F (1934) 38 °F (1905)
Yesterday 87 °F 56 °F
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hot tomorrow as well ped tomorrows highs
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304. SLU
Quoting stormchaser19:


Last year at this time of the year the environment was more hostile in the Atlantic...




And it also remained that way through mid-July which caused the convection to be highly suppressed in the MDR last year early in the season. Yet still it was able to produce an active Cape Verde season by August but most of the storms struggled to develop for the same reasons: low 400mb temps and dry air.
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Quoting PedleyCA:
MesoWest Jurupa Valley CA US SGXWFO, Riverside, California (PWS)
Updated: 1:49 PM PDT on May 11, 2013
Scattered Clouds
96 °F
Scattered Clouds
Humidity: 16%
Dew Point: 43 °F
Wind: 1 mph from the SW
Wind Gust: 9.0 mph
Pressure: 29.92 in (Falling)
Heat Index: 92 °F
Visibility: 10.0 miles
UV: 7 out of 16
Pollen: 5.10 out of 12
Pollen Forecast new!
Clouds:
Scattered Clouds 12000 ft
(Above Ground Level)
Elevation: 794 ft

The above are over an hour ago, I have 93.8F here and the Airport is 98F
yeah yer on the warm side again and we are going to the cold side

Toronto Pearson Int'l Airport
Date: 6:00 PM EDT Saturday 11 May 2013
Condition:Mostly Cloudy
Pressure:29.7 inches
Tendency:falling
Visibility:15 miles
Temperature:57.9°F
Dewpoint:46.4°F
Humidity:65%
Wind:SW 15 mph


tonights forecasted low is 37 tomorrows high may not break 50
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PedleyCA - I see it finally cooled off a little for you. :/
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MesoWest Jurupa Valley CA US SGXWFO, Riverside, California (PWS)
Updated: 1:49 PM PDT on May 11, 2013
Scattered Clouds
96 °F
Scattered Clouds
Humidity: 16%
Dew Point: 43 °F
Wind: 1 mph from the SW
Wind Gust: 9.0 mph
Pressure: 29.92 in (Falling)
Heat Index: 92 °F
Visibility: 10.0 miles
UV: 7 out of 16
Pollen: 5.10 out of 12
Pollen Forecast new!
Clouds:
Scattered Clouds 12000 ft
(Above Ground Level)
Elevation: 794 ft

The above are over an hour ago, I have 93.8F here and the Airport is 98F
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Quoting SLU:


Joe Bastardi was 100% correct when he said that the 400mb temperatures have a huge part to play in the season's overall activity levels.

Here are plots of the 400mb temperature anomalies for all inactive and active hurricane seasons from 1950 - 2012.

Note how in the inactive seasons that the 400mb temperature anomalies were well below average everywhere. Most of these seasons produced an ACE index of less than 50 which is unheard of since 1995.

Compare it with the next plot of all above average seasons since 1950 which shows higher-than-normal 400mb temperature anomalies especially in the deep tropics where most of the ACE is generated. Most of these seasons produced an ACE index of over 150 and includes some of the deadliest seasons of the modern era.

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Image and video hosting by TinyPic



Last year at this time of the year the environment was more hostile in the Atlantic...


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Quoting stormpetrol:
Interesting feature near 24N/65W.

Hey stormpetrol what's up long time we have not talked what do you tink of the Storm GFS predicting
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297. SLU
Quoting TropicalAnalystwx13:

I'm not disagreeing. Above-average mid-level temperatures are good for tropical cyclone development and intensification. It doesn't matter much before the season...especially the Cape Verde season...though.


It will be something to monitor as the season starts. So far for May the temperature is normal across the MDR but below average in the Gulf and north of 30 north.
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Quoting SLU:


Joe Bastardi was 100% correct when he said that the 400mb temperatures have a huge part to play in the season's overall activity levels.

Here are plots of the 400mb temperature anomalies for all inactive and active hurricane seasons from 1950 - 2012.

Note how in the inactive seasons that the 400mb temperature anomalies were well below average everywhere. Most of these seasons produced an ACE index of less than 50 which is unheard of since 1995.

Compare it with the next plot of all above average seasons since 1950 which shows higher-than-normal 400mb temperature anomalies especially in the deep tropics where most of the ACE is generated. Most of these seasons produced an ACE index of over 150 and includes some of the deadliest seasons of the modern era.

Image and video hosting by TinyPic

Image and video hosting by TinyPic


I'm not disagreeing. Above-average mid-level temperatures are good for tropical cyclone development and intensification. It doesn't matter much before the season...especially the Cape Verde season...though.
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Quoting TheChart:
I tend to favor climatology, despite the solutions in some GFS model long-range forecasts.

Western Caribbean development is not likely, although some disturbed weather may be evident.

TC


nothing worth hiding in a bunker for
what is happening at this time is all merely long range dipictions
that bear watchin for the simple fact
that its recurring dipictions
over a pre determine time frame
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Interesting feature near 24N/65W.
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Quoting FunnelVortex:


Who gave the models crack?


More like Meth.... But this is the time of the year where this happens -- been the same story the last several years.
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Quoting BaltimoreBrian:
Cute



Who gave the models crack?
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290. SLU
Quoting TropicalAnalystwx13:

He used those images in his forecast over a month ago. A more recent image shows anomalies aren't as impressive...though Joe was using a very low temperature interval (0.2C). I went with 0.5C.

It doesn't matter much right now anyways. The hurricane season of 2004 had negative anomalies all across the Main Development Region at this time.



Joe Bastardi was 100% correct when he said that the 400mb temperatures have a huge part to play in the season's overall activity levels.

Here are plots of the 400mb temperature anomalies for all inactive and active hurricane seasons from 1950 - 2012.

Note how in the inactive seasons that the 400mb temperature anomalies were well below average everywhere. Most of these seasons produced an ACE index of less than 50 which is unheard of since 1995.

Compare it with the next plot of all above average seasons since 1950 which shows higher-than-normal 400mb temperature anomalies especially in the deep tropics where most of the ACE is generated. Most of these seasons produced an ACE index of over 150 and includes some of the deadliest seasons of the modern era.

Image and video hosting by TinyPic

Image and video hosting by TinyPic

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Starting to notice the low level swirl show itself as the mid and upper level swirl moves away slowly. This is the main reason why the NHC has shown no interest as it should continue. It has certainly been something fun to watch.

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Quoting BaltimoreBrian:


In that case I'll go out for dinner and see how far the run has done when I get back.

Cool see you then
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18Z GFS 54HR out cold in the NE
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Quoting BaltimoreBrian:


It looks like it is going out to sea in that run. The 12Z run had it in the NW Caribbean.

I didn't say it was likely. I said it was cute :)


I know, was just commenting on the model lol
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Quoting TropicalAnalystwx13:
Spiked and back down.



Still got some work to do about this..



Here is the guilty party.

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Quoting NICycloneChaser:


A sub-994mb TS/Hurricane aiming at SE Florida one the 26th of May.

Unlikely.


It looks like it is going out to sea in that run. The 12Z run had it in the NW Caribbean.

I didn't say it was likely. I said it was cute :)
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Rain coming!:)
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Spiked and back down.



Still got some work to do about this..

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Quoting wunderkidcayman:
18Z GFS is now rolling now at 36H


In that case I'll go out for dinner and see how far the run has done when I get back.
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Quoting BaltimoreBrian:
Cute



A sub-994mb TS/Hurricane aiming at SE Florida one the 26th of May.

Unlikely.
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Quoting SFLWeatherman:
It is now it at 36HR


Funny how we said that same time
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Quoting BaltimoreBrian:
WSW winds in the teens means low level circ is closed.


Decent pressure fall compared to daily norm as well.

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18Z GFS is now rolling now at 36H
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It is now it at 36HR
Quoting TropicalAnalystwx13:

Today's 18z run should start soon.
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Quoting TropicalAnalystwx13:

"Little" being the operative word there.




Yeah, still pretty similar. However, it looks way better than last year.
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WSW winds in the teens means low level circ is closed.
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Quoting BaltimoreBrian:
Cute


Today's 18z run should start soon.
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Is the FIMM model showing the long range storm?
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.