Tropical weather analysis - June 21, 2013

By: KoritheMan , 4:15 AM GMT on June 22, 2013

Invest 94E

An area of low pressure centered several hundred miles south-southwest of Acapulco, Mexico is producing disorganized showers and thunderstorms.

Figure 1. Latest infrared satellite image of Invest 94E. Image credit: NOAA's Satellite Services Division (SSD).

The system is compromised of an elongated convective band to the south, and these bands appear to be attempting to wrap cyclonically into the low-level center. An earlier scatterometer pass showed a broad surface circulation with some evidence of westerly winds on the south side of the gyre. There is still a little northwesterly shear over the low as suggested by the cloud pattern inferred from satellite imagery, but these winds appear to be relaxing, and are less than they were yesterday. There is evidence on water vapor imagery of the subtropical jet lifting northward progressively, so this leads credibility to the model forecasts of a decrease in shear. This low has potential for development into a tropical depression during the next day or two as it moves slowly westward for the next 36-48 hours before turning west-northwest toward a weakness in the subtropical high near 115W. It should be emphasized that many of the dynamical models show some sort of binary interaction between this low and another low several hundred miles to the west, a situation which could easily throw a wrench into the track forecast.

Most of the intensity models bring this system to a Category 1 hurricane, and there is a possibility it could get a little stronger before moving into cooler water in four days, but that will depend on how fast it organizes over the next 24 hours.

Probability of development in 48 hours: 70%

Invest 95E

The area of low pressure I alluded to above has been tagged "Invest 95E" by the National Hurricane Center. This low is located about 750 miles south-southwest of the southern tip of Baja California.

Figure 2. Latest infrared satellite image of Invest 95E. Image credit: NOAA's Satellite Services Division (SSD).

Shower activity near this system is almost nonexistent, but scatterometer and satellite data suggest that the surface circulation associated with this system is fairly robust, although still rather broad. With the subtropical jet lifting north, there is not much evidence of vertical shear over the system, and the main issue with organization at the moment appears to be dry air and the broad nature of the circulation envelope. Otherwise, all systems are a go for gradual development of this low as it moves slowly westward to the south of a distant and weak mid-level ridge over the western United States.

In about four days, most of the models show some sort mutual interaction with Invest 94E. Given that 94E appears to be the more organized of the two, it is likely that 95E will dance around that system while gradually weakening, not the other way around. If the system doesn't interact strongly with 94E, it could get close to hurricane status, particularly since it will have about a day more over warm water than 94E.

Probability of development in 48 hours: 30%

Gulf of Mexico development possible during the first week of July

The GFS and its respective ensemble members have consistently shown lower pressures across the southern Gulf of Mexico/northwestern Caribbean area during the next 7 - 10 days, presumably in response to an increase in atmospheric moisture associated with the upward MJO pulse, which right now is enhancing convection in the eastern Pacific. Given the model forecasts of two tropical cyclones out of this pattern in the Pacific (a situation that actually has some evidence in the form of two invests), and the consistency of these models to forecast the upward MJO pulse into the western Atlantic sometime during the first week of July, I am inclined to believe there is a good possibility of a tropical cyclone forming out of this in the Atlantic later on.

The track of such a hypothetical system is still highly uncertain, and the pattern over the United States during that time is progressive, which often causes disagreement amongst the models as they struggle to resolve the pattern. This is the case now, with the majority of the GFS ensembles sending this system westward toward Mexico. The operational, however, has been consistent in bringing the modeled storm to the northern Gulf Coast from the Texas/Louisiana border to the western Florida panhandle in the long range. Again, don't focus on the exact track of a system we don't have yet, but based on the pattern in the models, there is a definite window of opportunity for whatever does develop (if anything) to move northward toward the northern Gulf Coast, which would be consistent with climatology as well. How strong such a system might get is just as uncertain, but given the upper wind pattern I see on the GFS, and extrapolating it to the time of the modeled storm, there is potential for a minimal hurricane. There is still evidence of upper tropospheric shear, particularly on the southwest quadrant of this system in the isobaric fields on the models, so if it does develop it will probably not be able to rapidly intensify, but it should be stronger than Barry.

While there is disagreement between the ensembles and the operational GFS, my experience as a 5 year forecaster have shown me that in the vast majority of cases, the operational tends to perform better in terms of track than the ensembles do, particularly when there is a sharp disagreement between the two like there is now. Recent examples include the GFS ensemble forecasts of a turn to the northern Gulf Coast with Hurricane Nate in 2011, when the operational insisted on a landfall in Mexico; and Hurricane Gustav in 2008, when the ensembles were all over the place from Pensacola to Houston. Once again, the operational won out on a landfall in Louisiana.

Regardless of whether or not this modeled system develops, it shows that the western Atlantic will soon become a spot for possible develop as pressures start to lower with the arrival of the upward MJO, which can once again be seen enhancing convection over the Pacific -- even the western Pacific, with several invests and a tropical storm.

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

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4. WunderAlertBot (Admin)
5:06 AM GMT on June 23, 2013
KoritheMan has created a new entry.
3. wxchaser97
6:30 AM GMT on June 22, 2013
Thanks Kori. I, too, believe the Atlantic will be getting active again.
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2. AtHomeInTX
4:54 AM GMT on June 22, 2013
Thanks Kori. Hope you're feeling better. Been noticing the ensembles too. Thanks for the tip about which did better with track. Learn something new every day. I like that at my age. :) Also noticed on tonight's 0z GFS something spinning up from the Atlantic entering the Caribbean albeit briefly looks like it could be a busy season.
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1. nigel20
4:41 AM GMT on June 22, 2013
The coming weeks will be very interesting. Thanks for the in-depth update Kori!
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Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.

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