Hurricane Dorian Discussion Number 23
NWS National Hurricane Center Miami FL AL052019
1100 PM AST Thu Aug 29, 2019
SUMMARY OF 1100 PM AST…0300 UTC…INFORMATION
ABOUT 295 MI…470 KM ENE OF THE SOUTHEASTERN BAHAMAS
ABOUT 580 MI…930 KM E OF THE NORTHWESTERN BAHAMAS
MAXIMUM SUSTAINED WINDS…105 MPH…165 KM/H
PRESENT MOVEMENT…NW OR 325 DEGREES AT 12 MPH…19 KM/H
MINIMUM CENTRAL PRESSURE…977 MB…28.85 INCHES
The NOAA and Air Force Reserve Hurricane Hunter aircraft have been tag-teaming the reconnaissance of Dorian tonight, providing useful information about what has changed during the past several hours. They found the pressure has dropped to about 977 MB, with recent SFMR data of about 90 kt (also supported by flight-level winds). These data are also consistent with satellite imagery that show Dorian with a larger, deeper central dense overcast than this afternoon. Thus the wind speed is raised to 90 kt on this advisory.
The initial motion is about the same as before, 325/10 kt. Dorian is expected to gradually turn to the west-northwest on Saturday, and westward on Sunday due to a building ridge over the southwestern Atlantic. While the model guidance generally shows this scenario in a broad sense, there are substantial timing differences among the guidance. The source of the uncertainty can be attributed to challenges in forecasting the strength and orientation of the mid-level ridge over the southeastern United States in a few days, along with exactly where and how large Dorian is by then. As you can imagine, with so many complex variables in play, it is no wonder the models have been having a difficult time nailing down the path of the hurricane. There’s been a notable trend on this model cycle toward a slower, more westward track beyond 36 hours, which can be seen most strongly in the GFS-based guidance. The track forecast is shifted southward beyond 36 hours and is about 30 n mi south of the previous one at 96 h. We will see if this southward trend in the models continues after the dropsonde data collected by the G-IV gets incorporated into the 00Z models. Users are reminded to not focus on the exact forecast track, as typical forecast errors at days 4 and 5 are around 155 and 205 miles, respectively.
There is still substantial middle- and upper-level dry air on the south side of the hurricane, as shown by tonight’s G-IV mission, which has been allowing only slow strengthening during the day. As Dorian turns west-northwestward, however, shear should drop somewhat due to it moving on the northeast side of an upper-level low near the Florida Straits, and the winds aloft will no longer be pointed toward the core, which will help decrease dry air entrainment. All these changes should promote intensification while Dorian moves over the 29C waters east of Florida, so the intensity forecast is raised from the previous one, consistent with the corrected-consensus guidance. Unfortunately, I don’t see any large-scale factors that would prevent Dorian from becoming an extremely dangerous category 4 hurricane during the next few days.
1. The risk of life-threatening storm surge and hurricane-force winds this weekend continues to increase in the northwestern Bahamas, and hurricane watches could be issued on Friday. Residents should have their hurricane plan in place and listen to the advice given by local emergency officials.
2. There is an increasing likelihood of life-threatening storm surge along portions of the Florida east coast late this weekend or early next week, although it is too soon to determine where the highest storm surge will occur. Residents should have their hurricane plan in place, know if they are in a hurricane evacuation zone, and listen to the advice given by local emergency officials.
3. The risk of devastating hurricane-force winds along the Florida east coast and peninsula late this weekend and early next week continues to increase, although it is too soon to determine where the strongest winds will occur.
4. Regardless of the exact track of Dorian, heavy rains are expected to occur over portions of the Bahamas, Florida, and elsewhere in the southeastern United States this weekend and into the middle of next week.