...Hurricane Harvey Current Trends and Expected Coastal Impacts...
Hurricane Harvey is forecast to continue in a general Northwest direction and make landfall generally between 1am and 3am on Saturday somewhere in the vicinity of Rockport, TX. The system will likely be a "major" hurricane at landfall, with extensive impacts from wind, storm surge and catastrophic fresh water flooding across much of the Texas coastal bend and adjacent coastal plain. Needless to say, travel is not recommended into that part of the state.
...Expected Movement of the System Once Inland and General Overview of Local Impacts...
Based on present indications, once the system makes landfall...the center is expected to drift Northwestward and come to a stop somewhere approximately 80 miles to the Southeast of San Antonio on Saturday afternoon. The system is then expected to remain nearly stationary into midday on Sunday before turning back toward the Southeast toward the coastal waters later Sunday into Monday. Assuming the stall-out and then Southeast recurve occurs as described above, the center of the system would remain to the East and/or Southeast of the local area at all times - and therefore the tendency for the most significant and heaviest rainfall would also generally be to the Southeast of the local area - generally to the East of I-35 and near/South of I-10. The below forecast impacts for the local area are based on this assumption.
...Local Rainfall Forecast and Potential Flooding Impacts...
Based on the above assumptions, we continue to forecast widespread average rainfall of 3-6 inches across most of the local area. Although scattered showers and isolated thunderstorms are possible as early as this afternoon and evening, the majority of the local rainfall will occur from after Midnight tonight into Sunday afternoon. As per the map at the top of this bulletin, the lower end of the forecast rainfall range would be in the Northwest part of the area, and the higher end toward the Southeast part of the area. Locally higher amounts are also possible in spots with any repeat heavier bands, especially near and/or East of I-35.
Rainfall of the amount currently forecast for the local area would mostly occur in the form of numerous showers and some scattered thunderstorms (thunderstorms are actually less dominant in tropical systems vs. regular showers). Some of the showers, however, are likely to produce periods of locally heavy downpours. It will be these downpours that are likely to result in flooding of especially low lying and poor drainage areas in at least some parts of the local region during the Advisory period, and especially during the day on Saturday into Saturday night and Sunday morning. 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 near and East of I-35, as noted above.
With the above in mind, at this time, we continue to forecast that the potential for the most significant creek, stream and/or river flooding would mainly exist further to the East of I-35 - to the East of the local area - and further to the South, closer to I-10 and Southward. Much higher rainfall totals in excess of 6-10 inches appear likely in those areas...and possibly over a more prolonged time period as well.
...Important Note on Potential Changes to the Rainfall and Flooding Impact Portion of the Forecast...
It is very important to note that should the center of Harvey shift significantly West/Northwestward vs. what is currently expected, and/or should the system stall out just to the Southeast of the local area for a longer time period (instead of turning back toward the coast as is currently anticipated), then the threat of more significant rainfall could potentially shift Westward into at least some parts of the local area. If this were to occur, the potential for flooding would increase across the local area as well (and the flooding potential could then be extended into Monday and possibly even Tuesday in such a case). While this particular scenario does not necessarily appear "likely" to occur at this time, the fact of the matter is that we won't be able to rule it out until we see how much inland progress the system makes on Saturday.
...Local Wind Impacts...
For the period 6am Saturday through 12 Noon on Sunday, look for East-Northeast winds to increase to 20-25 mph on a sustained basis, with frequent gusts of 25-35 mph. Some peak gusts of 35-40 mph are also possible at times, especially from midday Saturday into Saturday afternoon. This forecast is again based on the expected current track of the center of the system once it moves inland, as described in detail above. Please refer also to the latest update to the Wind Advisory product for additional details on that aspect of the forecast.
...Important Note on Potential Changes to the Wind Impact Portion of the Forecast...
It is very important to note that should the center of Harvey shift significantly West/Northwestward vs. what is currently expected once it has moved inland, then the threat of more significant wind gusts may develop locally over the weekend. Under such a scenario, sustained winds of around 30 mph with several gusts of 35-45 mph would be possible in some parts of the area, mainly from midday Saturday into Saturday afternoon. While this particular scenario does not necessarily appear "likely" to occur at this time, the fact of the matter is that we won't be able to rule it out until we see how much inland progress the system makes on Saturday.
We will continue monitoring the situation and issue updates as conditions warrant.
No comments:
Post a Comment