KoritheMan's WunderBlog

Tropical weather analysis - May 17, 2013

Posted by: KoritheMan, 5:41 AM GMT on May 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.

As of the most recent NHC advisory, the following information was contained on the cyclone:

Wind: 40 mph, with higher gusts
Location: 9.8°N 110.8°W
Movement: WNW at 14 mph
Pressure: 1006 mb

Alvin is extremely disorganized, and I am honestly having trouble distinguishing it from another ITCZ disturbance to the west.

Figure 1. Latest infrared satellite image of Tropical Storm Alvin. Image credit: NOAA's Satellite Services Division (SSD).

An earlier ASCAT pass suggested that the circulation had decayed into a sharp surface trough. Low cloud lines on shortwave infrared imagery are certainly not suggestive of an existing closed surface circulation, and evening microwave data reveals that even the mid-level center is beginning to lose definition. Westerly shear continues to affect Alvin, and the global models forecast this to continue throughout the forecast period. The GFS still stubbornly assumes that the upper tropospheric flow will improve and become mildly diffluent, but even that model is starting to recognize the presence of westerly shear within its 850-200 mb forecast fields. Given the hostile environment, Alvin is expected to degenerate into a remnant low within the next 48 hours, although it could occur much sooner if a closed circulation definitely does not exist. I will generously keep a distinct vorticity maximum throughout the five day forecast period, but I am not expecting Alvin to last that long after dissipation.

Alvin remains south of a weak mid-level ridge over southern Mexico. This is the primary steering mechanism for now, but the global models forecast a gradual turn to the west in about two or three days as Alvin becomes a shallower vortex and responds to the lower-tropospheric flow. Compared to yesterday, the model consensus is actually a consensus, and this increases confidence in my track forecast. I am well to the south of the National Hurricane Center forecast track as well as the model consensus given the likelihood that the cyclone no longer has a closed circulation. I could have gone even farther south, but at least some continuity with the models is desirable. Alvin -- or more likely its post-tropical remnants -- are anticipated to turn southwestward near the end of the forecast period while the mid-level center moves northward to northeastward ahead of the trough near Baja.

5-day intensity forecast

INIT 17/0300Z 35 KT 40 MPH
12H 17/1200Z 35 KT 40 MPH
24H 18/0000Z 30 KT 35 MPH
36H 18/1200Z 30 KT 35 MPH
48H 19/0000Z 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 20/0000Z 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 21/0000Z 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 22/0000Z 20 KT 25 MPH...POST-TROP/REMNT LOW

5-day track forecast

My 5-day forecast track for Alvin.

Elsewhere

There is the potential for long-range development in the Caribbean or western Atlantic if the long-range pattern in the GFS verifies, with a high over the southern United States, which will tend to focus convergence and upward motion farther south in tandem with the arrival of the upward MJO into this area of the world. I will probably not touch on this much, however, until the timeframe and pattern become more certain.

There is also a tropical wave moving westward across the central Atlantic south of 10N approaching 45W. While upper-level winds are not favorable for development in the Atlantic, this wave will need to be monitored for potential development when it enters the eastern Pacific in about a week.

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 May 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, 2:07 AM GMT on May 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 May 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 May 14, 2013

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Tropical Cyclone Report (TCR): Hurricane Carlotta

Posted by: KoritheMan, 12:11 AM GMT on April 29, 2013

Tropical Cyclone Report
Hurricane Carlotta
(EP032012)
14 June-16 June 2012

Carlotta was the easternmost landfalling tropical cyclone in the eastern North Pacific since reliable records of the basin began in 1966. Although short-lived, Carlotta was notable for its rapid intensificaton prior to crossing the southern coast of Mexico. Carlotta was responsible for three deaths, and its remnants appear to have contributed to the formation of Tropical Storm...

Categories:2012 East Pacific hurricane season

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