KoritheMan's WunderBlog

Tropical weather analysis - May 22, 2013

Posted by: KoritheMan, 01:38 AM GMT on mai 23, 2013

Invest 91E

I'm usually pretty good at catching things, but I missed this one. An area of disturbed weather has developed well to the south of the Mexican coast. The National Hurricane Center has officially designated this system as an "invest" (91E).

Following the typical progression of a disturbance in its early stages, deep convection has practically vanished, likely due to the diurnal minimum suppressing the development of deep convection. It could also have to do with the fact that the system still appears to be embedded in the ITCZ. The synoptic situation looks somewhat similar to Alvin, in that the large-scale environment is not the most conducive; the evolution of the upper-level winds will depend on how far south weak upper low south of Cabo San Lucas dives. Currently the models showing it moving northeast and decaying, which would favor a more conducive upper air pattern. Water vapor imagery shows fast upper-level winds a couple hundred miles to the west of the system, and there is some dry air in the vicinity of the disturbance. The GFS has changed its tune compared to a week ago and shows an environment that is more accurately diffluent than falsely anticyclonic. The CMC also shows a little bit of southwesterly shear during the early period before the upper flow transitions to a more uniform easterly regime. The SHIPS, which is based on the GFS, doesn't show much shear. Under the assumption that the westerlies may inflict more harm to 91E than the models are currently seeing, along with the disheveled nature of the system at present, I am going to withhold on mentioning the potential for a tropical cyclone for now. Interestingly, the normally aggressive GFS is not showing cyclogenesis from this disturbance, while the typically conservative ECMWF is.

The disturbance is currently south of a mid-level ridge. A small weakness is forecast to develop within the ridge to a trough over the southern United States, which may allow for the system to move more to the west-northwest over the next day or so. There are no apparent signs of this motion at the moment, however, and I feel the models may be a bit too far north with its trajectory. It should be noted that the upper-level flow looks a little more favorable the farther south the system stays, according to analysis of water vapor imagery and forecasts from the global models. The system is expected to turn back to the west in about three days, never threatening land.

Probability of development in 48 hours: 20%

Elsewhere

Elsewhere in the tropics, a tropical wave is currently in the southwestern Caribbean according to the 1800 UTC NHC surface map. This wave is enhancing convection across extreme northwestern South America and adjacent Central America. This wave has been consistently shown by the GFS and CMC to develop into a tropical cyclone that threatens southern Mexico in about six days. Given the consistency of this development in the GFS, which usually does extremely well with genesis forecasts (recall that it successfully foresaw the development of Alvin well before any of the other models), this wave will need to be carefully monitored for tropical development when it enters the eastern Pacific during the next day or two.

The 7-10 day pattern in the Atlantic continues to favor the possibility of tropical development in the western Caribbean. The upward MJO is slowly edging back into our area of the world, which of course favors enhanced precipitation. Simultaneously, the pattern during this period favors low-level convergence manifesting farther south, into the western Caribbean. Based on the 500 mb height anomaly pattern seen by the GFS during the 8 day forecast period, I see what I feel are three decent analogs for any potential tropical cyclone that develops in this region:

Abby (1968)
Arlene (2005)
Arthur (2008)

Figure 1. 500 mb height analogs for the 8 day forecast period as depicted by the 0z GFS. The analogs are given on the right.

I have no reason to favor one over the other at this time.

Categories:2013 Pacific hurricane season Invest 91E

Updated: 02:02 AM GMT on mai 23, 2013

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Tropical weather analysis - May 17, 2013

Posted by: KoritheMan, 05:41 AM GMT on mai 17, 2013

Alvin

Perhaps Simon will do better in 2014. In a bit of a surprise, westerly shear, associated with a large upper-level trough several hundred miles northwest of the tropical cyclone, began to increase over Alvin this morning. This shear has exposed the center to view, with Alvin generating only disorganized convection in broken bands southeast of the low-level center. Props to the ECMWF and CMC which anticipated this development several days ago.

Categories:2013 Pacific hurricane season Tropical Storm Alvin

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Tropical weather analysis - May 15, 2013

Posted by: KoritheMan, 11:59 PM GMT on mai 15, 2013

Alvin

Right on cue with the calendar, Tropical Storm Alvin formed today. As of the latest NHC advisory, the following information was available on the cyclone:

Wind: 40 mph, with higher gusts
Location: 8.7°N 105.1°W
Movement: WNW at 13 mph
Pressure: 1005 mb

Alvin looks well organized on satellite images, especially for a 35 kt tropical storm. Satellite estimates do not currently support an intensity higher than 35 kt...

Categories:2013 Pacific hurricane season Tropical Storm Alvin

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Tropical weather analysis - May 14, 2013

Posted by: KoritheMan, 02:07 AM GMT on mai 15, 2013

Invest 90E

A broad area of low pressure centered over the eastern Pacific about 650 miles south of Acapulco, Mexico continues to be a threat to eventually become a tropical cyclone.

The center is a little easier to locate this evening, possibly due to a somewhat better definition in the surface wind field compared to yesterday (as per low-cloud lines on last light visible satellite imagery). There is still not much evidence of vertical shear ov...

Categories:2013 Pacific hurricane season Invest 90E

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Tropical weather analysis - May 13, 2013

Posted by: KoritheMan, 12:43 AM GMT on mai 14, 2013

For the second year in a row, an offseason tropical disturbance has manifest in the eastern north Pacific basin. The National Hurricane Center (NHC) tagged this disturbance as an "invest" (90E) earlier today. This disturbance has the potential to develop into a tropical cyclone in the next few days.

Invest 90E

Satellite images suggest a fairly decent cloud pattern. I do not see any evidence of vertical shear over the system; in fact, a weak mid...

Categories:2013 Pacific hurricane season Invest 90E

Updated: 12:52 AM GMT on mai 14, 2013

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