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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172. VR46L
Quoting HurricaneDean07:

Okay? If dry air was shredding it, you would see a whole bunch of orange in the core, which there isn't. There is dry air to its west, so yeah that's a bit of a problem, still doesn't necessarily mean its dying right this instant. Maybe try to say its dying in about 6 or 7 more hours. I might believe you then.


If It becomes an invest I will happily eat crow !
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171. HadesGodWyvern (Mod)
India Meteorological Department
Tropical Cyclone Advisory #9
CYCLONIC STORM MAHASEN (BOB01-2013)
20:30 PM IST May 11 2013
==========================================

At 15:00 PM UTC, The Cyclonic Storm Mahasen over southeast Bay of Bengal moved northwestward and now lays near 8.5N 89.0E, about 420 km southwest of Car Nicobar, 880 km east southeast of Trincomalee, Sri Lanka, 1080 km southeast of Chennai, India, and 1560 km south southwest of Chittagong, Bangladesh.

the system would intensify further into a severe cyclonic storm during the next 24 hours. It would move initially northwestward during the next 36 hours and recurve thereafter northeastwards towards Bangladesh-Myanmar coast.

According to satellite imagery, The Dvorak intensity of Cyclonic Storm Mahasen is T2.5. It is a curved band pattern. Intense to very intense convection seen over south Bay of Bengal, adjoining Indian Ocean between 4.5N and 13.0N east of 82.0E. The lowest cloud top temperature due to convection is -70C.

3 minute sustained winds near the center is 40 knots with gusts of 50 knots. The central pressure of the system is 996 hPa. The state of the sea is high around the center of the system.
Member Since: May 24, 2006 Posts: 56 Comments: 50405
Quoting VR46L:


Dry air is shreding it





in the funktop image it started with deep colours but now is not



Agree with you that its chances of being classified anything are slim, though. :-)
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Im going to conserve on my Comments. I want to make my 4,000th comment on June 1. ;)
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Quoting VR46L:


Dry air is shreding it





in the funktop image it started with deep colours but now is not


Okay? If dry air was shredding it, you would see a whole bunch of orange in the core, which there isn't. There is dry air to its west, so yeah that's a bit of a problem, still doesn't necessarily mean its dying right this instant. Maybe try to say its dying in about 6 or 7 more hours. I might believe you then.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Member Since: July 15, 2006 Posts: 192 Comments: 59095
Quoting VR46L:


Dry air is shreding it





in the funktop image it started with deep colours but now is not



It's embedded within an upper low, so the dry air isn't quite as destructive as it normally would be. In fact, it's probably adding to the instability.
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Member Since: July 21, 2011 Posts: 83 Comments: 7167
164. VR46L
Quoting HurricaneDean07:

Theres no sign of 1. Decrease in convection 2. Displacement of center and 3. It has maintained/Increase vorticity and Convergence.

Don't know what youre seeing there, but I do agree it wont last for very long.


Dry air is shreding it





in the funktop image it started with deep colours but now is not

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163. Skyepony (Mod)
Haven't looked at the NESDIS-Star site in awhile. They updated it. Like how they linked Dr Masters' Quikscat RIP blog.

The QuikSCAT nominal mission ended on November 23, 2009. QuikSCAT was launched in 1999 and was already operating 7 years beyond its design life. The NASA/JPL press release and a blog that Jeff Masters wrote contain some additional information.
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Quoting Thrawst:
I wonder what the NHC forecasters do during the off-season. Do they play ping pong in the Air conditioning of the NHC or what? Maybe they do the tropical cyclone reports but what after that?


Outreach education: attending Hurricane Conferences (they spent the last week at the Florida Govenors conference in Ft. Lauderdale), so they have to prepare presentations for those type of conferences. They also get to spend a little time on the research side of things also. Imagine they also take their vacations during that time also.
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Quoting Dakster:
Will they issue a special tropical disturbance statement, if that happens?

I would imagine so, that's what they typically do.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Quoting Grothar:
Storm building up in South Florida.



Good Afternoon Gro.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Will they issue a special tropical disturbance statement, if that happens?
Member Since: March 10, 2006 Posts: 0 Comments: 11658
Storm building up in South Florida.


Member Since: July 17, 2009 Posts: 71 Comments: 28065
Quoting nrtiwlnvragn:
May have to switch to possible invest side......


Recent OSCAT



Still elongated to the SW due to the surface trough, but still very nice surface low developing.
Do I hear 90L initialization coming from the NHC?
maybe.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Quoting Skyepony:


According to this OSCAT sea level pressure is one of the data products derived from the Oceansat-2 Scatterometer (OSCAT) observations.


Finally...


Ya I clicked on that link about pressure and it took me to a page about Ice. Was wondering the details on how pressure is derived from the Scat.
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Quoting VR46L:



Sorry to be a kill joy but that blob is not going to make it its dying before my eyes IMO

Theres no sign of 1. Decrease in convection 2. Displacement of center and 3. It has maintained/Increase vorticity and Convergence.

Don't know what youre seeing there, but I do agree it wont last for very long.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Quoting Thrawst:
I wonder what the NHC forecasters do during the off-season. Do they play ping pong in the Air conditioning of the NHC or what? Maybe they do the tropical cyclone reports but what after that?


Lol. Plenty, I'm sure. They do research, upgrades to current equipment, add new equipment/tools, etc. I'm sure they stay just as busy.
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153. Skyepony (Mod)
Quoting nrtiwlnvragn:
Anyone know the details of the OSCAT Sea Level Pressure from manati.star? How is it measured, does it use a model for first guess, etc.




According to this OSCAT sea level pressure is one of the data products derived from the Oceansat-2 Scatterometer (OSCAT) observations.


You just beat me on the fresh OSCAT.

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May have to switch to possible invest side......


Recent OSCAT


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I wonder what the NHC forecasters do during the off-season. Do they play ping pong in the Air conditioning of the NHC or what? Maybe they do the tropical cyclone reports but what after that?
Member Since: July 18, 2010 Posts: 50 Comments: 1932
Latest wind shear map:

Member Since: July 21, 2011 Posts: 83 Comments: 7167
Quoting TropicalAnalystwx13:
Nice pre-season disturbance. It deserves some credit for trying at least, especially considering it's over sea surface temperatures of 25–26C and in an environment with wind shear of 30+ knots and dry air.

20 Knots now. Shears been decreasing. Like I said though, nice little hybrid system to get us prepared and ready for when Andrea Does decide to come around.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
148. VR46L
Quoting HurricaneDean07:


Key word, Expected.
If this thing continues on through tonight, the NHC will have to mention it. Still though, A neat little Hybrid disturbance to track, nonetheless.



Sorry to be a kill joy but that blob is not going to make it its dying before my eyes IMO
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Nice pre-season disturbance. It deserves some credit for trying at least, especially considering it's over sea surface temperatures of 25–26C and in an environment with wind shear of 30+ knots and dry air.
Member Since: July 6, 2010 Posts: 113 Comments: 34198
Quoting nrtiwlnvragn:
Marine Weather Discussion


Excerpt:


SHIP AND BUOY REPORTS VERIFY A LOW PRES CENTER DEVELOPED AT 24N66W
ALONG A TROUGH EXTENDING N FROM MONA PASSAGE. THE LOW IS
PROGRESSING E WITH CONVECTION ENHANCED ABOUT 90 NM E OF THE
CENTER. NE-E-SE WINDS ARE AT 20-25 KT WITHIN 360 NM OVER THE NE
SEMICIRCLE...WITH THE LATEST RAIN CONTAMINATED SCATTEROMETER
WINDS AT 20-30 KT. THE LOW WILL LIFT NE AND IS EXPECTED TO
DISSIPATE TONIGHT. THE TROUGH TO ITS S WILL DRIFT W ON SUN
REACHING THE SE BAHAMAS ON MON.


Key word, Expected.
If this thing continues on through tonight, the NHC will have to mention it. Still though, A neat little Hybrid disturbance to track, nonetheless.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Member Since: July 21, 2011 Posts: 83 Comments: 7167
Marine Weather Discussion


Excerpt:


SHIP AND BUOY REPORTS VERIFY A LOW PRES CENTER DEVELOPED AT 24N66W
ALONG A TROUGH EXTENDING N FROM MONA PASSAGE. THE LOW IS
PROGRESSING E WITH CONVECTION ENHANCED ABOUT 90 NM E OF THE
CENTER. NE-E-SE WINDS ARE AT 20-25 KT WITHIN 360 NM OVER THE NE
SEMICIRCLE...WITH THE LATEST RAIN CONTAMINATED SCATTEROMETER
WINDS AT 20-30 KT. THE LOW WILL LIFT NE AND IS EXPECTED TO
DISSIPATE TONIGHT. THE TROUGH TO ITS S WILL DRIFT W ON SUN
REACHING THE SE BAHAMAS ON MON.
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143. SLU
If this has a well defined COC, I'm willing to put my neck on the block and say it isn't far from being a subtropical depression.

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Member Since: July 21, 2011 Posts: 83 Comments: 7167
I think the most likely solution is that the surface low becomes misaligned with the upper trough and thus shears the system to death. However, I think it deserves at least a mention by the NHC.
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Shear Tendencies
Member Since: October 3, 2010 Posts: 40 Comments: 4129

2PM NHC tropical forecast discussion
THIS UPPER LOW LOCATED NEAR 24N66W SUPPORTS A
1012 MB SURFACE LOW PRES CENTERED NEAR 23N67W. SOME SHIP
OBSERVATIONS CONFIRMED THE PRESENCE OF THE SURFACE LOW THIS
MORNING. A TROUGH EXTENDS FROM THE LOW CENTER TO THE MONA
PASSAGE. THE SURFACE LOW IS FORECAST TO DRIFT TOWARD HISPANIOLA
ON SUN WHILE WEAKENING TO A TROUGH. THIS TROUGH WILL MOVE
WESTWARD.
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GFS believes that the system north of Puerto Rico is a symmetric, deep cold core low. But it might become a shallow warm core low.



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


I've seen little proof that this isn't entrenched at the surface. The upper low has completed the top to bottom transformation, from what I've seen. However, if it the upper low and the surface low become misaligned, then there's a problem.

I mean, in some ways this thing still has about a good 36 hours to work with before it starts to feel the affects of the encroaching frontal boundary.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
136. SLU
Quoting MississippiWx:


The NHC must be fairly confident that it won't last much longer. That's really the only thing I can think of that would keep them from at least tagging it an invest.


Let's give them til sun down to see if it persists and improves.
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Quoting AtHomeInTX:
Some lower pressure in the SW Caribbean at 240hrs. Maybe the beginnings of something?


The Euro is still a little to close in range to have the time period shown by the GFS, but give it a couple days, we can only look for hints right now.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Quoting nrtiwlnvragn:


You really expect development from that ull that has a little reflection to the surface?


I've seen little proof that this isn't entrenched at the surface. The upper low has completed the top to bottom transformation, from what I've seen. However, if it the upper low and the surface low become misaligned, then there's a problem.
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Some lower pressure in the SW Caribbean at 240hrs. Maybe the beginnings of something?

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Quoting MississippiWx:


Unfortunately, hurricane season doesn't wait on them. :-)


You really expect development from that ull that has a little reflection to the surface?
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Quoting nrtiwlnvragn:


Come oooooonnnnnn, give the Hurricane Specialists a last weekend off before they start 24/7 duty for the East Pacific season starting in a week.

True. just stating that we haven't actually seen an official Invest at all this season, that's a first, since like 4-5-6 Years ago. Even 2009 has some invests in the preseason.
One thing to Note.

Its under 20 knots of shear.
Convergence and Divergence is good, though weighted a little off to the east, Vorticity has increased.
I mean this thing looks better than the typical invest for this time of year.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
Quoting nrtiwlnvragn:


Come oooooonnnnnn, give the Hurricane Specialists a last weekend off before they start 24/7 duty for the East Pacific season starting in a week.


Unfortunately, hurricane season doesn't wait on them. :-)
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Quoting HurricaneDean07:
The low north of the Greater Antilles has Detatched from the frontal boundary. Initialized as 1012 MB low. Cmon NHC, get your crap together, if this was around last year it would've already been an invest.


Come oooooonnnnnn, give the Hurricane Specialists a last weekend off before they start 24/7 duty for the East Pacific season starting in a week.
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128. VR46L
Quoting HurricaneDean07:
The low north of the Greater Antilles has Detatched from the frontal boundary. Initialized as 1012 MB low. Cmon NHC, get your crap together, if this was around last year it would've already been an invest.


Its a waste of time and resources to call that an invest its dying IMO

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Anyone know the details of the OSCAT Sea Level Pressure from manati.star? How is it measured, does it use a model for first guess, etc.


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Looking better each update.

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Quoting HurricaneDean07:

The low north of the Greater Antilles has Detatched from the frontal boundary. Initialized as 1012 MB low. Cmon NHC, get your crap together, if this was around last year it would've already been an invest.


If this thing continues into tonight, expect the NHC to start mentioning it.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
124. VR46L
Quoting AtHomeInTX:


I'm really wondering if they're going to stop. :)


I dare say they will some time soon .. But I have no clue when !
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The low north of the Greater Antilles has Detatched from the frontal boundary. Initialized as 1012 MB low. Cmon NHC, get your crap together, if this was around last year it would've already been an invest.
Member Since: October 3, 2010 Posts: 40 Comments: 4129
122. JLPR2
Quoting Stormchaser2007:
Really doesn't look terrible.



They are probably going: "nah! it's still the 11th of May" XD
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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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