Invests Organizing in the Indian Ocean

By: MAweatherboy1 , 9:32 PM GMT on May 06, 2013

As we begin this new week, there has been little change in the global tropics over the past few days. The focus for potential tropical development continues to be on the Indian Ocean, both the northern and southern part of the basin. The more imminent threat for development is in the southern Indian Ocean, where an area of low pressure at low latitude (less than 5 degrees) and far from land is organizing. This low is invest 94S, and is moving slowly to the SW. Maximum sustained winds are estimated to be in the range of about 25-30mph. The Joint Typhoon Warning Center is giving 94S a "medium" chance of development in the next 24 hours. I would give 94S about a 40% chance of developing in the next 24 hours, but a 90% chance of development within 72 hours.

Figure 1: Invest 94S.

94S is currently in a marginal environment at best for strengthening, with wind shear of up to 25-35mph being the biggest issue for the developing storm. In addition, the low latitude of 94S is inhibiting its ability to spin, which is of course how cyclones develop. While these problems should prevent immediate development, both are likely to become less obstructive in the next 24-48 hours as shear begins to relax and 94S slowly gains latitude. Global models clearly want to develop this system, and now even the reliable ECMWF, which was very hesitant to show development a few days ago, is fully on board for tropical development. The two questions then become where will 94S go, and how strong will it get? For now, the motion is mostly SW. The system will likely move pretty slowly for the next couple days, and could take a more southerly turn before eventually settling on a more WSW track. This will take it in the general direction of Madagascar and southeast Africa. At this point, however, it appears more likely that the system will dive south before it has an opportunity to threaten these areas. Regarding strength, the models are showing above average agreement on fairly significant intensification of the storm. My very preliminary thinking is shown in figure 2. As always when forecasting on a system that hasn't even developed yet, confidence is quite low, and major changes are possible.

Figure 2: My forecast track and intensity for 94S, by no means an official forecast.

My track does not include what happens to 94S beyond that, but as I mentioned the most likely scenario is that it goes south and becomes extratropical.

92B Also a Threat to Develop
Tropical development is also being watched for in the northern Indian Ocean over the next few days. The most likely source of development would be invest 92B, located over the southern Bay of Bengal. In my previous blog I noted invest 91B as the potential area of low pressure to watch for development in the northern Indian. This is indeed still an invest, but it has moved west and is unlikely to develop. Basically replacing it is 92B, which is a new low just in its formative stages. The forecast for 92B is more high stakes than the forecast for 94S because unlike 94S, 92B is likely to impact populated areas if it develops. Neither the official forecasting agency for this region, the India Meteorological Department (IMD) nor the unofficial agency for the region, the Joint Typhoon Warning Center, is currently acknowledging this system as an imminent threat for development. I would give 92B a 10% chance of development in the next 24 hours. Whether or not 92B will develop is less certain than whether or not 94S will develop. The majority of models do develop, and substantially intensify, 92B, but as has been the case for days, the ECMWF model does not develop the system. Because of its reliable track record, I am reluctant to disregard its solution, though I am still expecting development. I give 92B a 70% chance of developing within 96 hours. Because of the significant uncertainty regarding this system's future, I have not yet made a forecast for 92B, but as I mentioned on my previous blog yesterday I do think the system will develop, and at this point I am still favoring southeast India as a landfall location. The big question mark is strength, and that is just too uncertain to guess at right now. Today's 12z GFS at 180 hours seems reasonable to me.

Figure 3: 12z GFS at 180 hours, courtesy of Levi's model page.

Figure 4: Invest 92B, showing a large area of disorganized, shallow convection.

I do not anticipate doing a new blog until at least Wednesday, but if development of this system becomes more certain I will include my forecast in the comments section, along with potential forecast updates on 94S.

Thank you as always for reading, and I hope you have a great week!


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7. WunderAlertBot (Admin)
11:35 PM GMT on May 14, 2013
MAweatherboy1 has created a new entry.
6. MAweatherboy1
8:43 PM GMT on May 08, 2013
Good afternoon. Here's an updated track for what is now cyclone 24S, with 40mph winds. As I suspected yesterday, the short term track had to come south, though the long term WSW motion still looks good. Confidence is quite low, however, as JTWC notes. In fact, the CMC is even suggesting this thing may not go west at all but actually head east. I can't see that happening at this point though. You'll also notice a decrease in the intensity forecast. The models have generally backed off on intensity, really not much more to say than that.

Here's JTWC's track, which is comparable to mine.

They show progressive strengthening to 75mph by the end of their forecast period. I disagree with that, however, as I see it peaking in 3-4 days at around 70mph, then leveling off and beginning to slowly weaken eventually:

92B is slowly organizing as well, I am now about 90% confident that it will develop within 72 hours. No forecast yet, but I am starting to favor areas farther north in India as potential landfall spots. More on this later.
Member Since: February 11, 2012 Posts: 93 Comments: 8900
5. MAweatherboy1
9:13 PM GMT on May 07, 2013
Quoting CycloneFreak:
At, We are actively monitoring 92B and its subsequent development. You are welcome to blog there and share your expertise.
Quoting originaldashman:
I'm here to invite you to our Weather blog on behalf of our Team Leader - Kea (India's most comprehensive accurate private weather system)

We will be happy to have you in our blog for the discussions on "Mahasen" - 92B in BOB


Thanks for the invites guys, I appreciate them and it seems like you have a nice little community over there. Unfortunately, I know very little about that region of the world and only focus on activity over there when there is potential for a significant cyclone. Most of the time I am focused on US weather such as Atlantic hurricane season.

Anyways, no big changes to report tonight. 94S is organizing, I'd say 50% chance of development within 24 hours but near 100% within 72 hours. 92B is organizing also, but I still have questions about it. I'm thinking 30% chance of development within 24 hours, 70% within 72 hours. Still no forecast for this one. For 94S, the forecast track still looks pretty good (maybe needs to come south a little in the short term) and intensity is a little more questionable than yesterday, it could need to be lowered some. I may have an updated track for that one later tonight.
Member Since: February 11, 2012 Posts: 93 Comments: 8900
4. vagaries
7:35 AM GMT on May 07, 2013
For us it seems the low designated as 92B will initially track Northwards and take the trough corridor..lets see...
Member Since: January 30, 2011 Posts: 0 Comments: 1
3. originaldashman
7:16 AM GMT on May 07, 2013
I'm here to invite you to our Weather blog on behalf of our Team Leader - Kea (India's most comprehensive accurate private weather system)

We will be happy to have you in our blog for the discussions on "Mahasen" - 92B in BOB

Member Since: May 7, 2013 Posts: 0 Comments: 0
2. CycloneFreak
3:55 AM GMT on May 07, 2013
At, We are actively monitoring 92B and its subsequent development. You are welcome to blog there and share your expertise.
Member Since: May 5, 2013 Posts: 0 Comments: 2
1. MAweatherboy1
10:44 PM GMT on May 06, 2013
The 18z GFS was quite interesting on the BoB storm. It really intensified it, all the way down to 938mb. Perhaps the more important thing, however, is that it did not weaken it much before landfall as many previous runs have, and instead takes it into southeast India as a potentially catastrophic 947mb monster at 183 hours:

Member Since: February 11, 2012 Posts: 93 Comments: 8900

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Average 20 year old weather nerd. Plymouth State University Meteorology, Class of 2018. NOAA Hollings scholar. Summer 2016 intern at NWS Boston.

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