Wednesday, June 21, 2017

Remnants of Cindy to pass over the Mid-South Friday

We've been keeping a close eye on (potential, then actual) Tropical Storm Cindy in the Gulf of Mexico the past few days. For the first time in several years, the remnants of a former tropical system are set to pass directly over the Mid-South. First, here is the latest forecast track of Cindy (click any image on this page for a larger version):

Latest forecast track of Cindy from the National Hurricane Center.

Forecast Path

As you can see from the graphic above, as of early Wednesday evening, Cindy is expected to make landfall early Thursday morning near Beaumont, TX, or along the TX/LA border. It will be a moderate tropical storm with maximum sustained wind near 45-50 mph when it makes landfall. From there, it heads north up the TX/LA border then begins a right turn Thursday night, heading into southern AR, That right turn continues, moving what will likely be Tropical Depression Cindy, over the Mid-South, if not Memphis proper, on Friday around mid-day. There are some model discrepancies on the exact track of the center of the low and the timing, but it will be during the day Friday.

Effects on the Mid-South

The effects here in the Mid-South will primarily be those that were problems to our south today - some gusty wind, not-insignificant rainfall which could lead to some flash flooding, and as with any landfalling/remnant tropical system, a few strong storms that could produce brief tornadoes. We'll take them one at a time.


Wind has not been a major factor even while Cindy was a tropical storm today. Strongest wind of up to 40-50 mph was primarily right near the center and in convective bands well removed east and north of the storm. Cindy will weaken after landfall, but we'll see breezy conditions (10-20 mph, some higher gusts) through Thursday night. On Friday, as the low approaches and depending on its exact track, some areas could see sustained wind of 20-30 mph with a few gusts to 40+ mph, mainly in convective (thunderstorm) bands and near the path of the low. By Friday evening, any strong wind will subside back to the baseline of 10-20 mph. Widespread power outages are not anticipated, but with a slightly weakened grid due to remaining tree limbs on lines, etc. from recent storms, sporadic or scattered outages are possible, mainly Friday.

Heavy rain and flooding

The primary threat from Cindy is, and will continue to be, periods of heavy rain and the potential for flash flooding. Timing of any "bands" or "slugs" of moisture is very difficult more than several hours out, so trying to pinpoint exact times of when they will occur is borderline futile. Suffice it to say, rain chances will be high from late tonight until the system passes late Friday, however it is not expected to rain hard the entire 2-day period.

For now, it appears showers will begin to overspread the area tonight with the first main band moving through early Thursday morning. After this round, there could be a lull during the mid-day hours tomorrow, although given the unstable and very moist atmosphere that is in place, scattered showers and thunderstorms are probably a decent bet. Another round could affect the metro late tomorrow into the early overnight Thursday night, though that may set up just to our north. (Again, this is not set in stone.) Then, indications are that we'll see one more period of rain, probably the heaviest, associated with the approach, passage, and departure of the low itself during the day Friday, quite possibly lasting into Friday evening. Again, this is HIGHLY subject to change. (If you have tickets to Live at the Garden Friday night or plan to attend a Levitt Shell concert, watch for information from those entities on their plans and stay tuned to the forecast. Even if it isn't raining during the concert times, conditions may be too wet leading up to the events to get them properly setup.)

Overall, rainfall totals could vary quite a bit from one place to another but are expected to generally fall in the 2-3" range between tonight and Saturday morning with some areas seeing up to 5". Flash flooding and urban ponding/flooding are possible. Flash Flood Watches are not currently in effect but I put odds at better than even that they will be before Friday. Our area is under a Moderate Risk of flash flooding for the Thursday night/Friday period, as shown below.

Rainfall projections from the NWS through Saturday morning show a band of 2-3" of rain expected across the metro. A few locations could see more, and possibly less, as these numbers are approximates. Memphis is just northeast of the 2-3" annotation in the center of the image. (NWS/WPC)

The Weather Prediction Center forecasts a Moderate Risk (10-15% chance) of flash flooding on Friday for the metro. (NOAA/WPC)

Brief tornadoes

Thunderstorms associated with remnant tropical systems build in highly-sheared environments where wind at various levels of the atmosphere is blowing briskly, and in varying directions. This can lead to the threat of spin-up tornadoes in some of these storms, even those that may not contain lightning or be severe by any other definition. (Storms from tropical systems tend to have much less lightning than a "normal" summertime thunderstorm and are also not as tall, but they can still pack a punch.) The greatest threat for any tornadoes will be to the right of the track of the storm. On Thursday, that threat will mainly be to the south of the metro in LA, southeast AR, and western MS where there is a Slight Risk of severe storms. The Memphis area is in a Marginal Risk on Thursday, meaning a few storms could contain brief damaging wind gusts or a spin-up tornado. (Hail is generally not a threat with tropical systems as their "core" is warm, not cold like classic low pressure systems.)

The Storm Prediction Center severe weather outlook for Thursday, showing the Slight Risk (where a tornado is most likely) south of the metro. (NOAA/SPC)
On Friday as the low passes near the metro moving northeast, the most favorable position for brief tornadoes will be in the southeast quadrant of the storm. If the low passes to our north, Memphis could be in that quadrant. If it passes just to the south or overhead, the favored area will be to our south. Currently, the Storm Prediction Center, based on the Hurricane Center track, places the Slight Risk south of Memphis with the metro in a Marginal Risk once again. That could change and will bear monitoring. Overall, the probability of tornadoes also will go down a bit from Thursday to Friday as the system weakens in general. As a last comment, the tornadoes associated with weak remnant systems in general are not the monsters we see in the Plains or Dixie Alley associated with supercells. They are more akin to the brief spin-up's that are possible with a squall line moving through, but we still need to prepare for the possibility that they could occur, and probably with little notice.

The Storm Prediction Center severe weather outlook for Thursday, showing the Slight Risk (where a tornado is most likely) southeast of the metro. (NOAA/SPC)

After the storm

By Friday night, it appears the worst will be over with perhaps a lingering shower that lasts until Saturday morning. Most of Saturday looks like it could be dry (though precipitation may hold back a little longer than current thinking) and Sunday introduces another conundrum, as computer models have fought like pre-teen siblings over whether an upper level system brings additional rain chances. Right now those chances appear fairly low. Stay tuned.

In the meantime, be sure to follow us on social media for the absolute latest on this dynamic weather situation; download the MWN app for radar, currents, the MWN Forecast, and our social feeds as well as StormWatch+ optional severe weather alerts; and check out the MWN Tropical page (optimized for desktop browsing) with more information on the current status and future of Cindy! All social and app links are listed below.

Erik Proseus
MWN Meteorologist

Follow MWN on Facebook, Twitter, and Google+
Visit on the web or on your mobile phone.
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

No comments: