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