Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 02:26 PM GMT on Ιούνιος 20, 2011
The outer spiral bands of intensifying Tropical Storm Beatriz have reached the coast of Mexico between Acapulco and Puerto Vallarta, and a hurricane warning is now in effect for the coast of Mexico from Zihuatanejo northwestward to La Fortuna. Beatriz is headed to the northwest under the influence of the large trough of low pressure over the Midwest U.S. that is causing severe weather and flooding rains there. As Beatriz nears the coast Tuesday morning, the trough may have progressed far enough eastwards so that Beatriz wil miss making a direct hit on the coast, and instead turn west and move out to sea as a ridge of high pressure builds in. Regardless of whether the core of the storm makes landfall or not, the major threat from Beatriz will be heavy rains. Rainfall amounts of 4 - 8 inches will be common along the coast, and up to a foot of rain is likely in some mountainous regions, causing significant flooding and dangerous mudslides. NHC is giving Manzanillo a 5% chance of experiencing hurricane-force winds of 74 mph or greater; these odds drop to just 1% for Puerto Vallarta, and 8% for Barra Navidad. With ocean temperatures between 29 - 30°C and wind shear predicted to drop to 10 knots later today, there is no reason why Beatriz couldn't intensify into a Category 1 hurricane by Tuesday. NHC is giving a 15% chance the Beatriz could intensify into a Category 2 or stronger hurricane. A hurricane hunter aircraft is scheduled to visit Beatriz this afternoon to gauge its strength. Satellite loops reveal that Beatriz has become more organized this morning, and Microwave satellite imagery indicates that Beatriz has built about 50% of an eyewall. Once this process is complete, more rapid strengthening is likely.
Figure 1. Morning satellite image of Tropical Storm Beatriz taken at 8am EDT June 20, 2011. Image credit: NASA/GSFC.
Significant severe weather outbreak and flooding rains possible today in the Midwest
Severe thunderstorms developed along a warm front stretching from Eastern Colorado through Nebraska and into Iowa and Wisconsin last night. The result was an active evening with numerous severe thunderstorm, tornado, and flash flood warnings. Hail to the size of baseballs and winds to 77 miles per hour were reported at Champion and Imperial, Nebraska. Many other locations reported large hail and winds greater than 60 miles per hour, and NOAA's Storm Prediction Center logged thirteen preliminary tornado reports in Nebraska, Colorado, Iowa, and Wisconsin. The large, slow-moving low pressure system responsible for yesterday's severe weather will touch off a new round of severe weather this afternoon, and the Storm Prediction Center has placed Eastern Nebraska, Western Iowa, and portions of three other states in their "Moderate Risk" area for severe weather. Baseball and softball-sized hail is likely in some of the stronger supercell thunderstorms that form, and there is also the risk of a few strong EF-2 and EF-3 tornadoes.
Figure 2. Today's severe risk outlook from NOAA's Storm Prediction Center.
Also of concern is the large area of 2 - 4 inches of rain this storm is likely to bring to the Missouri River watershed this week. As I discussed in detail in Friday's post, the flood control system on the Missouri River is being strained beyond its designed limits, and this week's rains are likely to worsen existing flooding and potentially cause new levee breaches on the river.
Figure 3. Predicted rainfall for the coming five days (top image) shows that a large region of 2 - 4 inches is expected over the Missouri River watershed (bottom image.) Image credit: NOAA/HPC and Wikipedia.
Critical fire conditions to give Arizona a break this week
Powerful southwest winds gusting to 50 mph affected much of Arizona yesterday, producing some of the worst fire conditions the parched state has seen all year. Sierra Vista in Southeast Arizona experienced sustained winds of 31 mph, gusting to 50 mph yesterday, causing a major spread of the dangerous Monument Fire. With air temperatures of 94° and a humidity of just 13%, it was a tough day for firefighting. The 33-square mile fire jumped fire control lines and surged into the town, forcing the evacuation of thousands of people. However, after a difficult 4-day stretch of critical fire conditions, the winds will give Arizona a break today. Winds under 10 mph are expected in Sierra Vista, and strong winds and critical fire conditions are not expected in the state until at least Friday, according to NOAA's Storm Prediction Center. This respite should give firefighters a chance to gain the upper hand on the three significant fires burning in the eastern part of the state. Arizona's largest fire on record, the massive 800-square mile Wallow Fire, should be mostly contained by the end of the week if this forecast holds up. According to our weather historian, Christopher C. Burt, the Wallow Fire is a long way from being the largest fire in U.S. history. That distinction belongs to the great Peshtigo Fire of 1871, which burned 5,938 square miles of Wisconsin and Michigan.
The Atlantic is quiet
The Atlantic is quiet, with no tropical cyclones predicted over the next seven days by the reliable computer models.
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