DFW: Gulf low may form, Tropical Storm Bill possible, heavy rain event expected

Latest Forecast ➡ A new post about Tropical Storm Bill was started to help improve readability.  All previous forecast updates in the three days leading up to Bill’s formation are archived below, in the order that they were written.

➡ Final Event Recap: As predicted, peak wind gusts of 50 mph and greater, and record rainfall hit North Texas. Read more.

Initial Event Summary [Posted Saturday 6/13] May 2015 was DFW’s wettest May on record and DFW’s third-wettest month of all-time (records date back 117 years to 1898).  Many areas experienced historical flooding. Lake Lewisville reached a record level, and many people across North Texas were evacuated from their homes.  Of course, the “official” statistics apply to DFW Airport, which received 16.96 inches of rain in May beating the previous May record by over 3 inches (or 24%).  However, many parts of North Texas received double the amount of rain that DFW Airport received. Parts of Cooke County, for example, received nearly 30 inches (the Gainesville COOP site 5 miles east of the Gainesville airport measured 28 inches).  Now, just two weeks after our wettest May on record, I fear that a storm will form in the Gulf of Mexico and move north into Texas.  This storm has not formed as of yet; however, I expect to see surface pressures begin to fall over the southern/central Gulf of Mexico through Sunday, and continue deepening through Monday as convection forms around the surface low.  Irrespective of its future status as a “tropical” storm or a general surface low, I believe that excessive rainfall amounts will be possible across the eastern 1/2 of Texas, north into Oklahoma.

Tidbit: If a tropical storm forms, it will be named Bill

Forecast Discussion #1 [Posted Saturday 6/13 at 12:45 pm]

For the past couple of days, the numerical prediction models have consistently indicated that an area of low pressure will form Gulf of Mexico and move ashore early next week (Mon/Tue). The track of this system would bring it across North Texas on Tuesday, with a plume of very heavy rain on its northern/eastern periphery. If this materializes, we could be looking at yet another heavy rain event in North Texas. Again, I’m discussing (and attempting to forecast) the evolution and non-linear motion of something that doesn’t even exist. Right now, we have nothing more than an atmospheric perturbation that could deepen over the Gulf of Mexico over the next 24-36 hours, with subsequent thunderstorm formation and heavy rainfall as the surface low forms and moves northwestward. This is something that you will want to stay aware of and check back for future updates. For now, I will just refer to this as an area of low pressure. I have to say that in the numerical data, it *appears* to have tropical characteristics and it wouldn’t be too far-fetched to suggest that a tropical depression and/or tropical storm may be in the making. I will leave that to the NHC to determine and I will follow their lead; however, folks from the Texas coast northward into North Texas should stay weather aware and check back for updates. Irrespective of the type of system, we need to monitor the potential for significant rainfall in North Texas early next week.

Discussion #2 Posted Saturday 6/13 at 4 pm

I rarely share model data because of their highly technical nature. However, this is a near-term event that may affect recently-flooded areas. To illustrate the potential track of the surface low that may bring heavy rain to recently-flooded areas, I have decided to display a “spaghetti plot” of the latest numerical model tracks.

Because of the inter/intramodel consistency over the past 3 days, I have high confidence that a surface low will form and bring heavy rain to areas along/near the track. This includes North Texas. I believe the best rainfall coverage will be in the Monday night through Tuesday time frame here in N. TX. Until the storm actually develops, I can’t be any more specific than that. The greatest rainfall coverage still appears to be the eastern 1/2 of North Texas.

The National Hurricane Center has scheduled a reconnaissance mission for Monday morning (6/15) to investigate. If a closed circulation is found with maximum sustained winds meeting depression/storm criteria, a status will be assigned and advisories will likely be issued for the Texas Coast. Stay aware of this developing situation. Even if a “tropical” status isn’t assigned, this system may still bring heavy rainfall along the path depicted in the spaghetti plot.

The image below shows:
● Spaghetti Plot of Latest Model Tracks
● Storm Has Not Formed Yet
● May Develop Over Gulf Within 36 Hours
● Hurricane Hunters to Investigate Monday AM
● Heavy Rain Event Along Path Mon – Wed
Do NOT focus on the exact path/center – Areal rainfall coverage either side of its path will be large

"Spaghetti plot" of model-simulated tracks of surface low that is likely to form in the Gulf of Mexico by Monday (June 15). This low could become a tropical depression/storm pending the findings of a Hurricane Hunter mission scheduled for Monday morning.
Prepared Saturday June 13 at 3 pm: “Spaghetti plot” of model-simulated storm tracks. Low is likely to form in the Gulf of Mexico by Monday (June 15). This could become a tropical depression/storm pending the findings of the recon mission scheduled for Monday 6/15.

Discussion #3 Posted Monday 6/15 at 11:20 am

***Heavy Rain Event Tuesday – Wednesday***
***Rainfall Amounts: 3 to 5 Inches, Locally Higher***
***Flash Flooding and Areal Flooding Likely***
***Preparations Should Be Rushed to Completion***

Note: The next two updates (Discussion #4 and Discussion #5) tie into this one, just posted later in the day on Monday 6/15…

This will be a short update.  I’ve been discussing the potential for a surface low forming in the Gulf of Mexico that could become a tropical system. This appears to be happening and recent satellite imagery reveals a large and expanding area of convection (thunderstorms) associated with this system.

The Hurricane Hunters are investigating. It could become a tropical storm within the next 12 to 24 hours. Even if it doesn’t “officially” get assigned tropical status, I still expect substantial rainfall amounts Tuesday through Wednesday, which will have a significant impact on North Texas (especially recently-flooded areas). Stay aware of this developing situation.

If you live in an area that was flooded in May or still experiencing flooding, preparations for this system should be rushed to completion. I imagine that a Flash Flood Watch will be issued today. This rainfall map represents my *best* estimate after poring over a ton of data. It will be subject to change, but overall there are no changes to my previous thinking. If I had drawn a rainfall map two days ago, it would have looked like this; I chose to wait for additional data.

For North Texas, showers may begin to approach from the south late tonight. However, the heaviest rain appears to be tomorrow afternoon through Wednesday morning.

High temperatures: Upper 70s for both Tuesday and Wednesday.

Update [Monday 6/15 at 10 pm CDT] Tropical Storm Bill has formed as expected. My forecast for heavy rain in North Texas remains the same.

Prepared Monday 6/15 11:20 am CDT: Our predicted rainfall amounts through noon Wednesday (6/17).
Prepared Monday 6/15 11:20 am CDT: Our predicted rainfall amounts through noon Wednesday (6/17).

Discussion #4 Posted Monday 6/15 at 3:10 pm

Statement from the National Hurricane Center:
NHC is not planning to initiate advisories on the [Gulf] system at 5 PM. Next aircraft will [investigate] before 8 PM

With the aircraft mission at 8 pm, I believe a circulation will be found. If that is the case, the NHC will initiate Tropical Storm Watches/Warnings for the Texas Coast. I will have updates later this evening.  Also, a Flash Flood Watch may be issued by the NWS in Fort Worth soon.  /End-Update

Update [Monday 6/15 at 10 pm CDT] Tropical Storm Bill has formed as expected. My forecast for heavy rain in North Texas remains the same.

Discussion #5 Posted Monday 6/15 at 3:30 pm

***Flash Flood Watch has been issued for most of North Texas effective until 7 pm Thursday (6/18)***

Posted Monday 6/15 3:30 pm: Flash Flood Watch in effect until 7 pm Thursday 6/18.
Posted Monday 6/15 3:30 pm: Flash Flood Watch in effect until 7 pm Thursday 6/18.

Discussion #6 Posted Monday 6/15 at 10:00 pm

***Tropical Storm Bill Has Formed***

As I’ve discussed in my previous forecast updates, the National Hurricane Center deployed several Hurricane Hunter missions to investigate the area of disturbed weather in the Gulf of Mexico today.  The initial mission found sufficient winds, but they were unable to identify a closed circulation in the surface wind field.  The evening mission was successful and a slightly-elongated, closed circulation was found.  The NHC made that announcement in their routine, 10 pm CDT forecast update and they immediately initiated advisories on Tropical Storm Bill.

Tuesday 6/16 at 1:30 am (Graphical Update):  Tropical Storm Bill will make landfall today (Tuesday).  There are NO changes to any of my previous forecasts from the past few days (documented above).

Remember: Do NOT focus on the track of the center.  The lines on this illustration represent the model-simulated tracks of Bill’s center of circulation, not the heaviest rain. With this storm, the heaviest rain will be east of the center… encompassing nearly all of North Texas later today through tomorrow (Wednesday).  This is a very common configuration with tropical storms and a complex lesson in physics that would easily require its own post. Typically, the heaviest rain and even isolated/brief tornadoes tend to the right of the storm’s forward motion (if you are driving down the road, the passenger would be sitting to the right of your forward motion).

Tropical Storm Bill at 1 am CDT Tuesday 6/16/15. No changes to my forecast.
Tropical Storm Bill at 1 am CDT Tuesday 6/16/15. No changes to my forecast.

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