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Tropical weather analysis - May 23, 2013

By: KoritheMan , 4:01 AM GMT on May 24, 2013

Invest 91E

The area of low pressure located about 550 miles south-southwest of Acapulco, Mexico remains poorly-organized. A fortuitous microwave overpass captured the system just after 00z, and showed that the low-level center is broad and ill-defined; an ASCAT overpass confirmed a similar signature. There is a pronounced area of concentrated rotation within the convective ball from 8 to 9N, but analysis of satellite imagery suggests that this circulation is a mid-level vortex, and the actual low-level center is closer to 10N.

Figure 1. Latest infrared satellite image of Invest 91E. Image credit: NOAA's Satellite Services Division (SSD).

There are some southwesterlies ahead of the system as per water vapor images, but these winds appear to be gradually moving westward ahead of 91E. The GFS, CMC, and SHIPS continue to maintain a fairly light upper tropospheric shear regime over the system, this flow in fact appears lighter in today's model runs. Nevertheless, the system is close enough to upper-level westerlies that I am going to be a little cautious. Conditions appear favorable for slow development, although the close proximity of the system to the monsoon trough could be an inhibiting factor to rapid development. There is also some dry air around.

The system remains south of a low- to mid-level ridge over the Gulf of Mexico. Normally this would favor a path toward the west-northwest given the amplitude of the ridge. However, 91E is far enough to the south that I anticipate a more uniform westward movement over the next several days; while the system might gain a degree or so of latitude during the next 72 hours, any significant poleward component of motion will likely have to wait until days four and five, when a larger-scale trough begins to amplify over the western United States as per the global models. This system is not forecast to threaten land, although the 12z ECMWF has an interesting binary interaction toward the coast between this feature and a tropical wave behind it that is expected to become a tropical cyclone in the global model sea level pressure fields. This should be taken as an interesting triviality, and not an accurate portrayal of reality.

Probability of development in 48 hours 30%


The NHC has officially removed the tropical wave we've been tracking over the last several days from the 1800/0000 UTC surface charts, portraying instead a feature that has gotten absorbed into the cyclonic gyre associated with the monsoon trough. I can't find any easy evidence of a tropical wave either, but regardless of the nominal status of the system, this is the one the global models have been consistently transforming into a tropical cyclone during the next several days. Extrapolation of the tropical wave's position relative to recent days would place it in the vicinity of the far eastern Pacific right now, which would be consistent with a broad area of cyclonic turning noted near 8 to 9N near 90W.

Conditions appear quite conducive for development for this wave as it moves off to the west-northwest. Interests along the southern coast of Mexico should be aware of a possible tropical cyclone in the next five to seven days, as the large-scale pattern continues to favor a landfall along the south coast of Mexico from Acapulco to Puerto Angel.

On the Atlantic side of things, the large-scale 7-10 day pattern continues to favor the possibility of some sort of tropical development -- or at least the formation of a broad area of low pressure -- in the western Caribbean. The GFS and Canadian ensembles -- as well as the operational -- show increasing heights over the southern United States, which would tend to lower pressures farther south in the Caribbean, and consequently cause an increase in surface convergence, which is beneficial for the development of thunderstorms. This would be coincident with the entrance of the upward MJO into that area during that time, and it would also coincide with climatology. It is possible that whatever is left of the eastern Pacific tropical wave/purported tropical cyclone will help to initiate the development of this disturbance, similar to how the mid-level remnants of Hurricane Carlotta assisted in the formation of Atlantic Tropical Storm Debby almost one year ago. This is a complex meteorological situation that, while climatological, also tends to cause enhanced convective feedback issues amongst the global models as they react to all this increased moisture, which introduces a lot of uncertainty into the forecast.

Nevertheless, the GFS has slowly come into better agreement on the timing of this potential development, showing a tropical cyclone in the western Caribbean east of the Yucatan Peninsula around the June 3 to 4 timeframe over the last several model cycles. Again, we may not get a cyclone out of this, but the large-scale pattern is definitely shaping up to be a wet one in this region. The potential track of such a system is still up in the air, but the operational GFS shows it being a threat somewhere along the United States Gulf Coast; climatology would favor a smooth shot into peninsular Florida, but it could just as easily go westward into Central America or Mexico under such a fickle and complex pattern.

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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7. WunderAlertBot (Admin)
12:47 AM GMT on May 25, 2013
KoritheMan has created a new entry.
6. zampaz
11:17 AM GMT on May 24, 2013
Good work on explaining the basis of your conjectures.
Others may come to different conclusions from the same information and this in turn may lead to fun and fruitful discussions with those who are better informed than I. Wanted to give you a nod to the good presentation.
I lurk the wunderground.

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5. KoritheMan
5:53 AM GMT on May 24, 2013
Quoting MississippiWx:
Nice blog, Kori, I guess. ;-)

Psst. You know it is.
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4. MississippiWx
4:41 AM GMT on May 24, 2013
Nice blog, Kori, I guess. ;-)
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3. VirginIslandsVisitor
4:09 AM GMT on May 24, 2013
Thanks for the interesting read, Kori!

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2. Civicane49
4:08 AM GMT on May 24, 2013
Thanks, Kori.
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1. Bluestorm5
4:07 AM GMT on May 24, 2013
Thanks for update!
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Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.

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