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 , 4:47 PM GMT on August 04, 2011
Tropical Storm Emily remains unorganized this morning, and continues to linger just south of Haiti, near 17.3°N, 72.3°W. Emily is 90 miles south of Port au Prince, Haiti. Storm motion over the past 24 hours has been slow, varying between completely stopped and west to west-northwest at 5 mph. This motion (or lack thereof) is still something that the models aren't analyzing well. Satellite imagery shows that thunderstorm activity on the north side of Emily seems to be disrupted, possibly by the terrain of Hispaniola, but also potentially by the continued moderate shear to the north of the storm. Wind shear has weakened to the northwest of the storm in the past 24 hours, but it will probably not be enough to allow Emily to undergo any significant intensification. The layer of dry air that we've been talking about for the past few days has also all but dissipated to the west and north of the storm. As the National Hurricane Center has been forecasting, environmental conditions are becoming slightly more favorable for the storm. Satellite estimates of wind motion suggest that low level circulation in the storm has become very broad and extends north over Hispaniola, which indicates that there's potential for the storm to undergo a quick jump to the north, but overall the storm remains weak and this seems unlikely. Emily continues to be tilted to the east with height, but doesn't appear as sheared as yesterday morning.
Conditions in Hispaniola have surely deteriorated over the past 24 hours, however, thunderstorm activity appears to have weakened over the island this morning. Infrared satellite imagery shows that cloud tops have warmed in the past 6 hours on the north side of the storm, which means that strong thunderstorms are no longer building high into the atmosphere. High resolution model forecasts (see Figure 1) have continued to predict that the heaviest rain will fall to the east of the storm. The longer Emily tracks west without taking a significant turn to the northwest, the more likely it is that Haiti will see the most extreme rainfall in the storm. Overall, 6 to 12 inches of rain is expected to fall, with local amounts up to 20 inches possible in higher terrain. Flash floods and mudslides are a serious threat.
Figure 1. Forecast radar and sea level pressure from the 06Z (2am EDT) run of the HWRF high resolution model. While I think that the model was initialized poorly and doesn't accurately represent where the storm will travel over the next 24 hours, I do think that the precipitation field is accurate. The strongest rain and winds have been on the east and north sides of the storm over the past couple of days. If Emily continues to move west before taking a significant turn to the northwest, Haiti could receive the strongest impact from the storm.
Forecast for Tropical Storm Emily
Models continue to waver back and forth on Emily's forecast track. Yesterday evening, the HWRF model forecast Emily to cross over Hispaniola and undergoing a close encounter with the Florida coastline. Last night, the National Hurricane Center wrote that "if Emily does not begin its northwestward turn soon…a watch could be required for parts of southern Florida today." Since the storm appears to be moving slightly more to the north than west this morning, this doesn't look like it will be necessary, although the forecast remains very uncertain. In today's 06Z runs, both the HWRF and the GFDL are probably forecasting Emily to move too far north in the next 12 hours. Given the present direction and speed of the storm, it's hard to see these two models' forecasts coming to fruition. The official forecast track from the National Hurricane Center is a turn to the northwest over the next 6 to 12 hours, with landfall in Haiti happening this afternoon. Beyond that, they forecast Emily to stay on a northwest course through the Bahamas, where Emily could restrengthen a bit before making a turn to the northeast on Sunday, although they qualify this forecast with the fact that it's very uncertain, and that the global models dissipate Emily after crossing Hispaniola. The official forecast track does not have Emily making any landfall in Florida, but the Miami to West Palm Beach area is still within the cone of uncertainty.
Interestingly, the models that have done the best job at predicting the track of Emily thus far are the less relied-on statistical track models—those that don't take into account any current atmospheric dynamics. If Emily remains on a west to west-northwest track today, we cannot rule out that it cross over a larger area of Cuba, approaching the southeast portion of Florida. However, given the amount of land interaction in this potential track, the probability of Emily remaining a tropical cyclone in this scenario is low.
Figure 2. Satellite imagery of Tropical Storm Emily at 10:15am EDT. The strongest thunderstorm activity is now in the southern portion of the storm. Thunderstorms over Hispaniola appeared to weaken this morning.
Typhoon Muifa continues to be a category 2 typhoon on the Saffir-Simpson scale. Satellite imagery shows a well developed storm that is moving west-northwest. Over the next day, Muifa is expect to turn to the northwest as it approaches China. Today's track forecast is more north and east of yesterday's, with a brief landfall just north of Shanghai, potentially as a category 3.
Figure 3. MODIS satellite imagery of Typhoon Muifa from earlier today, plotted using NASA's new Rapid Response Web Mapping Service.
Central U.S. heatwave
The heat continues for the central U.S., where I've heard reports that local media in the region were canceling all of their outdoor shots because of the dangerous conditions. Here are some of yesterday's extreme temperatures, which were compiled by our weather historian, Christopher C. Burt:
Little Rock, Arkansas set an all-time record with 114°F (the old record was 112°F set in 1986). Fort Smith, Arkansas set an all time record of 115°F (the old record was 113°F set both Tuesday and previously in 1936).
State maximum air temperatures from Wednesday:
• Arkansas: 116° at Silver Hill (4° short of state all-time record)
• Oklahoma: 115° at Atoka
• Louisiana: 111° at Caney
• Texas: 111° at Fort Worth and Wichita Falls (that also had a record high minimum of 88° this morning)
• Missouri: 109° at Branson and Ava
The heat index is also at play in this heat wave; some incredible values recorded yesterday include 126° in Poplar Bluff, Missouri, 125° in Walnut Ridge, Arkansas, and 122° in Arkadelphia, Arkansas. The GFS continues to forecast heat index values around 120° in the lower Mississippi Valley through the weekend.
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