Barbara heading to southern Mexico; 91E over the Pacific

By: Civicane49 , 6:11 AM GMT on May 29, 2013

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Tropical Storm Barbara has formed and is approaching to the Mexican coast along the Gulf of Tehuantepec. With the development of this second named storm, this year is the second consecutive year for the eastern Pacific to feature two named storms in the month of May. In addition, this year is tied with 2012, 2007, 1984, and 1956 for featuring the most named storms in the eastern Pacific on May. According to the latest National Hurricane Center advisory, Barbara has winds of 50 mph and a minimum pressure of 1000 mb. It is moving slowly moving northeastward at 3 mph and is centered about 120 miles south-southwest of Salina Cruz, Mexico. The structure of Barbara is continuing to improve considerably with a more symmetric appearance, organized spiral bands around it, and a good central dense overcast (CDO) on satellite images. The Puerto Angel radar currently depicts part of the cyclone’s southern eyewall.

Forecast for Barbara
Barbara should continue to intensify before making landfall in the Mexican coast. The tropical cyclone is embedded in a highly conducive environment with very warm sea surface temperatures of near 30°C, low wind shear of 5 to 10 knots, and the relative humidity value of 70%, which is pretty moist. So, there is no reason why the system should not continue to strengthen further. Given its rather small inner core, the current structure of the storm, and the aforementioned conditions, the cyclone should intensify in a rather quick pace and reach as a high-end tropical storm before making landfall roughly in the next 18 hours; in fact, the SHIPS model gave a 71% chance of a 25 knot increase within 24 hours. However, the cyclone has very limited time to strengthen, so I have some doubts that it will briefly become a hurricane. But it is possible. After it moves over land, it will weaken rapidly and later dissipate over the mountainous terrain of Mexico.

Barbara will continue to move slowly north-northeastward through a split in the mid-level ridge. As the trough deepens over the southern United States, it should increase its forward speed by tomorrow or so. The system is expected to make landfall on the Mexican coast along the Gulf of Tehuantepec by 18 hours. It will continue to move north-northwestward through Mexico and whatever is left of it could move into the Bay of Campeche. The biggest threat of this storm is the heavy rain. Since the cyclone will move in a rather slow pace and interacting with the mountainous terrain, the heavy rain would result in life-threatening flash floods and mudslides to parts of southern Mexico and Guatemala. Interests in this area should remain monitoring the progress of this tropical storm.


Figure 1. Water vapor imagery of Tropical Storm Barbara. Image credit: Mauna Kea Weather Center (MKWC).

Invest 91E becoming better organized
A persistent area of low pressure (Invest 91E) located about 850 miles south-southwest of the southern tip of Baja California has become better organized than it was yesterday. The cloud pattern has slightly improved and the low-level center became better defined on the recent scatterometer pass. Nonetheless, the system remains fairly disorganized; satellite loop shows a moderate easterly shear continuing to shift the convection away from the partially exposed low-level center.

Forecast for 91E
Further development of 91E appears to be possible as conditions will remain marginally favorable to support it in the next several days. The shear is expected to gradually lessen over the system during the next few days, which should become less of a problem for it to develop. However, the large area of dry air to the north of the low would limit convective activity for the system and disrupt its organization. By 48 hours, the system is forecast to cross into cool sea surface temperature of below 26.5°C threshold needed for tropical cyclones. The system will likely dissipate by days four or five within unfavorable conditions combined with dry airmass and cool waters. All things considered, I give this system a 40% chance of becoming a tropical cyclone in the next 48 hours. 91E is anticipated to move slowly north or north-northeastward in the next several days as the mid-latitude trough amplifies over the southern United States. The system is unlikely to be a significant threat to land.


Figure 2. Evening infrared satellite image of Invest 91E. Image credit: NOAA/RAMMB.

Elsewhere in the tropics
Although no global models are forecasting tropical cyclone development in the Atlantic, the GFS/ECMWF/CMC ensembles have been consistent in predicting the lowering pressures across much of the western Atlantic in early June. In addition, shear is forecast to decrease gradually across the Caribbean by next week, allowing any development to occur. The upward Madden Julian Oscillation (MJO) pulse is moving into the western Atlantic and would remain in that region until early June. The upward MJO pulse helps enhance convection and lower pressure across much of the western Atlantic as seen on water vapor imagery, showing a lot of moisture in this area. Development remains a possibility there.

Civicane49

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2. WunderAlertBot (Admin)
2:50 PM GMT on June 04, 2013
Civicane49 has created a new entry.
1. nigel20
6:17 AM GMT on May 29, 2013
Thanks Civicane!
Member Since: November 6, 2010 Posts: 12 Comments: 8424

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