Heat's here, and a "Suspicious Swirl"

Posted Updated
Hvy R 27 May 11
Mike Moss

High temperatures at the Raleigh-Durham airport reached our old record of 94 on Monday, then came up a little short of the record of 97 Tuesday afternoon (we reached 95 there, while Fayetteville, Elizabeth City and Lumberton all made it to 99, and Rocky Mount and Wilmington managed 97).  The upper ridge that helped boost the temperatures so far above normal should weaken and retreat a bit over the next couple of days, but appears likely to reorient itself in such a way as to drive temperature back up some over the weekend. The run of 90+ temperatures last week, together with our month-ending mid 90s, didn't result in a record-setting May by any means, but it did leave us with a May that ranked 9th warmest out of 67 so far at the Raleigh-Durham airport.

In the midst of the recent run of hot temperatures, we did have two rounds of substantial shower and thunderstorm activity, the one last Friday leading to flash flooding for some areas over the western half or so of the viewing area, and the next on Saturday shifting to the east and mainly affecting the coastal plain. You can see maps of the rainfall totals, based on a combinations of rain gauges and radar estimates, in the first two images above. While we remain below normal for rainfall in many areas for the year, we have had just enough across much of the area that we've stayed in "abnormally dry" rather than drought conditions, though some places south and west of the Triangle, and more recently over the coastal plain, have been in "moderate drought" in the estimation of the U.S. Drought monitor. The heat this week, and potentially into early next week, could potentially push more of the area back into a drought designation if rainfall is as sparse as models make it appear for the next week or so. The heat exacerbates the problem of course, as it dries out the ground, increases evaporation from reservoirs, and also tends to boost water usage rates.

We may have at least a shot at a brief respite this Friday. It isn't a "lock" yet, but recent model projections indicate a stronger push of cooler and less humid air into the region Thursday night than was earlier anticipated, and if that holds up we could see highs in the mid to upper 80s, and better yet, dew points falling into the 50s, which means no difference in the temperature and the heat index! If this pans out, enjoy it, since temperature and humidity appears poised to climb again over the weekend.

One last tidbit - today is the start of hurricane season, and appropriately enough a disturbance that moved east across the northern U.S. as a cluster of thunderstorms and weak swirl of low pressure then turned to the right and has been moving south off the east coast. This morning, it developed a symmetric upper level outflow that looked characteristic of a transition to a more tropical nature (see the satellite photo in the third image). While it shouldn't affect our state, the National Hurricane Center is now rating it as having about a 30% chance of becoming a tropical cyclone, so it will be interesting to see if it becomes Tropical Depression One as it heads toward northern Florida and then into the Gulf of Mexico, or, while unlikely, manages to become Tropical Storm Arlene.

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