...General Overview...
The center of Hurricane Harvey will continue to meander around (with a very slow, erratic movement) in the area to the South of I-10 generally 50-75 miles to the Southeast of San Antonio through tonight and/or Sunday morning. An area of high pressure moving into the region from the West will start to push the system back toward the East/Southeast by midday and into the afternoon hours on Sunday.
Widespread rain will continue across the local area through much of the day Sunday, before tapering off from the West by around 6pm on Sunday. Locally heavy rainfall is possible at times mainly today through Sunday morning. Where the exact bands of heavier rain tends to set up from time to time will determine who receives the most rain, but with this update we have re-oriented the forecast rainfall totals (see map at top of this bulletin) to match the GENERAL trends of heavier rain banding thus far today, and what is expected through tomorrow.
In general, we still expect the highest rainfall and greatest potential for significant flooding on a widespread basis to remain just to the East of the area, further to the East of I-35, with the main concern (with regard to flooding) locally being low lying/poor drainage areas, specifically the typical problem low water crossings. This will especially be an issue near and to the East of I-35 based on present trends (which is really not a significant change from earlier updates).
Gusty East/Northeast winds will continue into Sunday morning, and will then gradually decrease.
Please see below for much more details on both wind and rain across the local area.
...Local Rainfall Forecast and Potential Flooding Impacts...
Very generally speaking, we are forecasting average total rainfall through 6pm Sunday (since pre-dawn Saturday) of 3-8 inches across the local area. The lower end of the range will be in far Western sections, with the higher end in far Eastern sections (see map at the top of this bulletin). Generally speaking, the highest totals (as well as the greatest level of uncertainty surrounding those totals) are expected to occur immediately along and to the East of I-35, generally from near/North of San Marcos through Kyle and Buda and then into the central third of the Austin Metro. In that narrow band (shown in red on the above image) we are forecasting 6-8 inches of rain on average, but this is highly dependent on exactly where heavier bands of precipitation tend to set up from time to time through Sunday. It is possible that some locations within that band will receive less than the indicated amount, and it is also possible that other locations within the same band may receive slightly higher than the indicated amount, depending on where the heavier precipitation bands set up.
To the East of the aforementioned line - further to the East of I-35 - widespread 8-10 inch (and higher) amounts are expected (as shown in purple on the above image), as we've forecast for several days now.
At this time, the primary flooding concern for the majority of the local region continues to be in/near low lying and poor drainage areas (especially low water crossings and the like) at times through Sunday. Any parts of the area that receive repeat episodes of locally heavy downpours would be particularly vulnerable to such flooding, especially at low water crossings and similar areas. This would be even more likely to occur closer and to the East of I-35, as described in greater detail above.
One other note on the rainfall forecast. We are aware that there are multiple sources of information floating around in the media, on social media, etc. that show a wide range of very high rainfall totals being forecast for the local area. Please be aware that our forecast here, as indicated on the map at the top of the bulletin, covers the period from pre-dawn today (when the rain really began) through 6pm on Sunday. We expect the rain to decrease in coverage and intensity for a time starting then, but there will be additional rain produced by this system later next week when it recurves back toward the region once again (we will provide additional details on that in later updates). Keep in mind that some of these media sourced rainfall forecast maps include "Storm Total" rainfall, which would add the amounts of this weekend to the amounts that are expected later next week (since it's from the same "storm") and present that on a single map. The point we're trying to make is that it's important to keep in mind the valid time periods of the product you're looking at, as some outlets may not provide or clarify what that time period may be, so we'd advise using caution when viewing any rainfall forecast that does not specify the time period being covered by the forecast (especially those that use the term "Storm Total" or similar).
...Local Wind Impacts...
On average, look for East-Northeast winds of 20-25 mph to continue on a sustained basis, with frequent gusts of 25-35 mph through Sunday morning. Some peak gusts of 35-40 mph are also possible at times, especially from midday today into this afternoon. During this same time period, a few peak gusts of 40-45 mph cannot be ruled out, especially in far Southeastern portions of the local region (i.e., toward the San Marcos area and points South and Southeast from there).
...Important Note on Potential Changes to the Rainfall and Wind Forecast...
It is important to note that should the center of Harvey shift significantly West/Northwestward vs. what is currently expected, or should the system fail to turn back to the Southeast tomorrow as is currently expected, then both the rainfall and/or wind forecasts above may require revision (generally upward and/or for a longer time period). For that matter, the system could also meander further Eastward than expected which would result in a potential reduction and/or decrease in duration of both wind and rain across the area. While neither of these scenarios necessarily appear "likely" at this time, we will continue monitoring trends closely and issue updates if a change becomes likely or apparent.
We will continue monitoring the situation and issue updates as conditions warrant.
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