KoritheMan's WunderBlog

Tropical Cyclone Report (TCR): Hurricane Carlotta

By: KoritheMan, 12:11 AM GMT on April 29, 2013

Tropical Cyclone Report
Hurricane Carlotta
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 Debby in the Gulf of Mexico several days later.

a. Synoptic History

The origin of Carlotta was complex, and a little uncertain. The African Easterly Jet (AEJ) was rather active over the eastern Atlantic during the last week of May through the first week of June. Several small-scale convective systems moved westward off the coast of Africa within this pattern, at times resembling tropical waves. Based primarily on continuity of a complex of showers and thunderstorms that possessed an accompanying area of lower- to middle- tropospheric rotation, it may be possible to link a weak tropical wave back to the coast of Africa on 2 June. The associated shower activity associated with this wave was virtually nonexistent, and when it moved off the coast, any convection was most likely linked to the ITCZ. Thereafter, the wave became indistinguishable as it encountered a highly subsident airmass over the tropical Atlantic, and it is possible that this wave dissipated sometime subsequent to 6 June. Meanwhile, convection increased significantly over the eastern North Pacific from about 10 to 5N 100 to 110W beginning late on 8 June; this abrupt increase in convection was probably induced by an eastward-moving Kelvin wave that was propagating through the region. Shower activity began increasing over the western Caribbean the next day. Surface data was inconclusive regarding the existence of the earlier tropical wave, but if it was a still a distinct entity within the lower- to middle- tropospheric wind fields at that point, it most likely entered the eastern Pacific from Central America late on 10 June. Shower activity increased over the far eastern portion of the basin the next day, but the associated convection was poorly-organized. A broad area of low pressure formed with the system several hundred miles of the coast of Guatemala late on 12 June. Banding features developed the next day, and the system continued to gain organization. It became a tropical depression near 0000 UTC 14 June while centered approximately 400 miles southeast of Salina Cruz, Mexico.

Convective banding increased, and the system became a tropical storm near 0600 UTC. Around 24 hours after becoming a tropical storm, central banding increased around a ragged eye, and Carlotta is presumed to have become a hurricane at that time. Carlotta moved northwestward toward the coast of southern Mexico toward a weakness in the subtropical ridge over the Gulf of Mexico. Located within a very favorable environment characterized by low vertical wind shear and higher lower- to middle- tropospheric relative humidity values, and deep warm waters, Carlotta underwent a period of rapid intensification. Carlotta reached its peak intensity as a 100 kt major hurricane hurricane around 2015 UTC 15 June while centered about 85 miles southeast of Huatulco, Mexico. Thereafter, the eye became less distinct, and, possibly due to local topographic effects from the mountains of southern Mexico, Carlotta weakened a little, to an intensity of 90 kt, by the time the center made landfall near Huatulco on the coast of southeastern Mexico around 0115 UTC 16 June. Carlotta rapidly weakened after it moved inland, and it was reduced to a remnant low pressure area by 1800 UTC that day, centered over central Mexico about 75 miles west of Chilpancingo. The mid-level remnants of Carlotta moved northeastward into the southern Gulf of Mexico and northwestern Caribbean Sea where they contributed to a large and complex area of disturbed weather that spawned Tropical Storm Debby in the Atlantic a few days later.

b. Meteorological Statisics

Observations in Carlotta (Figs 2 and 3) include the satellite-based Dvorak intensity technique from the Tropical Analysis and Forecast Branch (TAFB), the Satellite Analysis Branch (SAB), and from University of Wisconsin CIMSS (UW-CIMSS). Several ASCAT passes, and to a lesser extent, microwave data, were also useful in tracking Carlotta. A reconnaissance mission was conducted into Carlotta on 15 June near the time of peak intensity, and this data was also incorporated into the best track of the tropical cyclone. The doppler radar station at Puerto Angel was also useful in tracking the center of Carlotta, which was very well-defined on that radar as it approached the Mexican coast.

Carlotta's peak intensity is a little uncertain. There is some variation in the subjective and objective satellite estimates during the time of peak intensity, with the estimates ranging from the upper end of category one intensity, to the lower end of category four. The latter estimates were from the CIMSS ADT algorithm, and based on the satellite and radar presentation, appear to be the most reliable of the group. In addition, a reconnaissance aircraft flew into the eye of Carlotta late on 15 June, and found reliable SFMR winds of 97 kt. While the data is far from conclusive, there appears to be enough evidence to posthumously upgrade Carlotta to a major hurricane for a brief time on 15 June. The hurricane began to weaken shortly thereafter.

Sustained hurricane force winds were not reported on land, but this is typical for landfalling tropical cyclones. Wind gusts to hurricane force persisted for nearly two hours at Pluma Hidalgo in the state of Oaxaca.

The hurricane also produced heavy rainfall, with a storm maximum of 13.78 inches in Tuxtepec, which is also located in Oaxaca.

There was one ship report of tropical storm force winds associated with Carlotta. The ship Decisive (call sign V7D17) reported a sustained wind of 37 kt at 2100 UTC 14 June.

c. Casualty and Damage Statistics

Three deaths can be directly attributed to Carlotta. A 13-year-old girl and her 7-year-old sister were killed in the town of Pluma Hidalgo in the Mexican state of Oaxaca when the mud-brick house they were staying in collapsed. In addition, a 56-year-old woman from the coastal city of San Jose Manialtepec was killed when her vehicle flipped over under the force of strong winds. Unofficial reports document that as much as 7 people were killed in the storm, but it is impossible to determine whether these deaths were direct.

While Carlotta was a fairly potent hurricane, overall damage appears minimal. As much as 29,000 homes and 2,500 businesses were affected in Mexico. It should be noted, however, that the state of Oaxaca requested as much as 1.444 billion pesos ($13 million USD) in assistance for the purposes of repairing public infrastructure.

d. Forecast and Warning Critique

The genesis of Carlotta was not well forecast, probably due to the rather rapid transformation into a tropical cyclone. The precursor disturbance was first mentioned in Tropical Weather Outlooks (TWOs) early on 13 June, and given a "high" chance (60%) of development. Probabilities reached 100% around the time of genesis as denoted in post-season analysis.

Since Carlotta was a short-lived hurricane, forecasts for it are difficult to evaluate. The track forecasts were excellent, with average errors of less than 50 miles for the two and three-day periods. This is probably due to the strong model agreement that was calling for a landfall in the Puerto Angel area. Intensity forecasts were not as good. Carlotta was correctly anticipated to become a hurricane before landfall, but as is typically the case, the rapid intensificaton of the hurricane was not well forecast.

A hurricane warning was issued at 1500 UTC 14 June from Puerto Angel to Maldonado. This was about eight hours before landfall.

Visible satellite image of Carlotta at peak intensity.

2012 East Pacific hurricane season

Tropical Cyclone Report (TCR): Hurricane Bud

By: KoritheMan, 12:10 AM GMT on April 29, 2013

Tropical Cyclone Report
Hurricane Bud
20 May-26 May 2012

Bud was an early season major hurricane that briefly reached category three intensity (on the Saffir-Simpson Hurricane Scale). It threatened the Puerto Vallarta area of Mexico but dissipated just offshore. Bud was the earliest formation of the second named storm in the eastern North Pacific on record, and the second named storm to develop in the basin during May 2012.

a. Synoptic History

Synoptic data indicate that the tropical wave which spawned Bud moved off the African coast on 5 May. Aided by the Intertropical Convergence Zone (ITCZ), the wave produced little deep convection on its own as it moved westward across the Atlantic south of 10N. The wave interacted with an upper-level trough over the eastern Caribbean Sea, which resulted in an increase in shower activity in that region on 10 May. A large-scale cyclonic circulation existed over the southwestern Caribbean into the eastern Pacific during this time, which makes distinguishing the tropical wave a little harder subsequent to 10 May. The wave crossed Central America into the eastern north Pacific late on 14 May. The large system began to acquire signs of organization in satellite images on 16 May, and a broad area of low pressure is estimated to have formed along the wave axis near 1200 UTC that day. The system was slow to organize over the next several days as it moved generally westward to the south of a strong mid-level ridge over the western Caribbean and Gulf of Mexico, possibly due to moderate easterly shear on the south side of this ridge. A reduction in the shear allowed the low to consolidate and become a tropical depression near 1800 UTC 20 May while centered about 450 miles south of Acapulco, Mexico. The cyclone became a tropical storm about 24 hours later.

Bud's initial development was rather slow, perhaps due to continued easterly shear caused by the Gulf of Mexico high pressure area and a smaller disturbance to the east. Bud finally became a hurricane near 0000 UTC 24 May. Development quickly became rapid as upper-level outflow improved and an anticyclone became established; this process was perhaps aided by a rather deep longwave trough moving through the southwestern United States. A well-defined eye appeared in satellite images near 1200 UTC that day, and Bud became a major hurricane at that time. The 100 kt intensity assigned to Bud at this time turned out to be its maximum intensity. Near 1800 UTC, when the satellite presentation was the greatest, Bud was centered approximately 300 miles southwest of Manzanillo and had begun to move northeast under the influence of the longwave trough.

Initially threatening the Mexican coast with relative ferocity, Bud began to weaken as southwesterly shear slowly increased ahead of the upper-level trough. The hurricane weakened rather quickly, undergoing a dramatic intensity reduction of 70 kt within the 24 hr period beginning 0000 UTC 25 May and ending 0000 UTC 26 May. A mere six hours later, Bud was reduced to a remnant low pressure area while centered offshore the southwest coast of Mexico just west of Puerto Vallarta. The remnant mid-level circulation quickly moved inland while the low-level center remained over water and dissipated.

b. Meteorological Statisics

Observations in Bud (Figs 2 and 3) include the satellite-based Dvorak intensity technique by the Tropical Analysis and Forecast Branch (TAFB) and the Satellite Analysis Branch (SAB). Objective CIMSS ADT estimates were also useful in constructing the best track of Bud, and for assessing the tropical cyclone's intensity. A couple of ASCAT passes from 25 to 26 May were particularly helpful in determining the progressive decay of Bud's low-level circulation as it approached the coast. In addition, two flights by a reconnaissance aircraft were conducted into Bud on 24 May. Data from these flights indicate flight-level winds that were supportive of winds at or near major hurricane strength.

Bud's peak intensity of 100 kt is based on Dvorak numbers that were generally in the 5.5 range from TAFB and SAB. CIMSS ADT estimates were as high as 115 kt, but these appear to be too high based on the aircraft data.

Bud produced locally heavy rains over portions of southwest Mexico, but there were no reports of tropical storm force winds.

c. Casualty and Damage Statistics

There have been no reported damage or casualties associated with Bud.

d. Forecast and Warning Critique

The formation of Bud was generally well forecast, although the timing of formation was difficult and inconsistent. The precursor disturbance was first mentioned early on 16 May and given a "low" chance (10%) of development in the enusing 48 hr. About 24 hours later, genesis probabilities increased to the "medium" category (40%), with forecasts reaching the "high" category (60%) early on 18 May. The low became disorganized later that day, and genesis forecasts were lowered accordingly, back down to the "low" category. When the system reorganized on 20 May, genesis probabilities were once again increased to the "medium" threshold. However, forecasts never reached the "high" category subsequent to this point all the way up to when genesis occurred.

Visible satellite image of Bud at peak intensity on 24 May.

2012 East Pacific hurricane season

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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About KoritheMan

Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.

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