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Hurricane Dorian Forecast Discussion Number 25
2019-08-30 16:49:55| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Fri Aug 30 2019 000 WTNT45 KNHC 301449 TCDAT5 Hurricane Dorian Discussion Number 25 NWS National Hurricane Center Miami FL AL052019 1100 AM AST Fri Aug 30 2019 Both Air Force and NOAA aircraft have been sending data from Dorian this morning. The flight-level winds from both planes have peaks at 100 kt and the SFMR measured 94 kt. The minimum central pressure has been oscillating between 972 and 976 mb. On this basis, the initial intensity has been set to 95 kt. The upper-low currently over Cuba which has been inducing some shear over Dorian is moving away from the hurricane, and the upper-level flow pattern is evolving toward a more favorable environment. In fact, the eye is becoming apparent on visible images as we speak and in radar data from the NOAA P3 aircraft. Consequently, the NHC forecast calls for additional intensification, and Dorian is expected to become an extremely dangerous major hurricane soon with additional strengthening likely as it heads for the northwestern Bahamas and the Florida peninsula. Fixes from both reconnaissance planes indicate that Dorian is moving toward the northwest of 310 degrees at 9 kt. As the upper-low over Cuba moves westward and a strong subtropical ridge builds over the western Atlantic as indicated by global models, the hurricane should be forced to turn west-northwestward and westward on a track toward the northwestern Bahamas and the Florida peninsula. By the end of the forecast period, the ridge is forecast to erode and the steering currents will weaken, resulting in Dorian slowing down considerably near and over the Florida peninsula. This increases the uncertainty in the track forecast during the 4- to -5 day period, and also will lead to a prolonged duration of wind, storm surge, and rainfall. The official forecast has been very consistent so far, and this one is very similar to the previous NHC forecast. It follows the multi-model and corrected consensus, and is in the middle of the guidance envelope. Key Messages: 1. Life-threatening storm surge and devastating hurricane-force winds are likely in portions of the northwestern Bahamas, where a hurricane watch is in effect. Residents should execute their hurricane plan and listen to advice given by local emergency officials. 2. Life-threatening storm surge and devastating hurricane-force winds are likely along portions of the Florida east coast by early next week, but it is too soon to determine where the highest storm surge and winds will occur. Residents should have their hurricane plan in place, know if they are in a hurricane evacuation zone, and listen to advice given by local emergency officials. 3. A prolonged period of storm surge, high winds and rainfall is likely in portions of Florida into next week, including the possibility of hurricane-force winds over inland portions of the Florida peninsula. 4. Heavy rains are expected over portions of the Bahamas, Florida, and elsewhere in the southeastern United States this weekend into the middle of next week. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 24.5N 69.8W 95 KT 110 MPH 12H 31/0000Z 25.3N 71.0W 105 KT 120 MPH 24H 31/1200Z 25.9N 72.7W 110 KT 125 MPH 36H 01/0000Z 26.3N 74.5W 115 KT 130 MPH 48H 01/1200Z 26.6N 76.1W 115 KT 130 MPH 72H 02/1200Z 26.8N 78.6W 120 KT 140 MPH 96H 03/1200Z 27.0N 80.4W 110 KT 125 MPH...INLAND 120H 04/1200Z 29.0N 81.5W 65 KT 75 MPH...INLAND $$ Forecaster Avila
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Hurricane Dorian Forecast Discussion Number 24
2019-08-30 10:54:55| National Hurricane Center (Atlantic)
Issued at 500 AM AST Fri Aug 30 2019 000 WTNT45 KNHC 300854 TCDAT5 Hurricane Dorian Discussion Number 24 NWS National Hurricane Center Miami FL AL052019 500 AM AST Fri Aug 30 2019 There hasn't been a lot of new data since the Hurricane Hunter planes departed Dorian several hours ago. The convective pattern on infrared satellite imagery has been nearly steady state, although the latest Dvorak estimates from TAFB and SAB rose to T5.0/90 kt. These estimates, combined with the earlier aircraft data, support maintaining an initial intensity of 90 kt. Dorian's heading is very gradually turning toward the left, with the latest estimate northwestward, or 320 degrees at 10 kt. Dorian is now being steered between a mid-tropospheric high centered near Bermuda and a mid-/upper-level low located over the Bahamas. The high is expected to expand westward, with a blocking ridge becoming established over the western Atlantic during the next several days. With the exception of COAMPS-TC and HMON, the other reliable models are in excellent agreement through day 3, with Dorian turning westward south of the ridge and moving near or over the northernmost islands in the Bahamas Sunday and Monday. After day 3, steering currents collapse as a break develops in the ridge, and Dorian will likely slow down considerably as it approaches the Florida peninsula. There is more spread among the deterministic models and their ensemble members during that time, with disagreement on exactly when and where Dorian will turn northwestward and northward on days 4 and 5. That being said, the tracks of the simple and corrected consensus models on this cycle did not warrant much change to the official NHC forecast, with perhaps just a slight southward adjustment on days 3 and 4. The biggest concern will be Dorian's slow motion when it is near Florida, placing some areas of the state at an increasing risk of a prolonged, drawn-out event of strong winds, dangerous storm surge, and heavy rainfall. The upper-level low to the west of Dorian continues to impart some southwesterly shear over the hurricane, which has prevented it from strengthening rapidly. However, Dorian is expected to enter a more favorable upper-level environment during the next 24 hours, which should allow its structure to become more well developed. Although overall the environment ahead of the storm appears conducive for strengthening, some models (in particular the ECMWF) suggest that some northerly shear could come into play while Dorian moves through the northwestern Bahamas, and for that reason the NHC official intensity forecast is not quite as bullish as the HCCA, Florida State Superensemble, and HWRF models. Still, Dorian is forecast to become a dangerous major hurricane later and maintain that status as it heads for the northwestern Bahamas and the Florida peninsula. Key Messages: 1. A Hurricane Watch is now in effect for the northwestern Bahamas, where the risk of life-threatening storm surge and hurricane-force winds this weekend has continued to increase. Residents should begin to execute their hurricane plans and listen to advice given by local emergency officials. 2. There is an increasing likelihood of a prolonged period of hazardous weather conditions that could last for a couple of days in parts of Florida early next week. 3. The risk of life-threatening storm surge along portions of the Florida east coast has increased, although it is too soon to determine where the highest storm surge will occur. The risk of devastating hurricane-force winds along the Florida east coast and peninsula early next week has also increased, although it is too soon to determine where the strongest winds will occur. Residents should have their hurricane plan in place, know if they are in a hurricane evacuation zone, and listen to advice given by local emergency officials. 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. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 23.8N 69.1W 90 KT 105 MPH 12H 30/1800Z 24.8N 70.3W 100 KT 115 MPH 24H 31/0600Z 25.6N 72.0W 105 KT 120 MPH 36H 31/1800Z 26.1N 73.8W 110 KT 125 MPH 48H 01/0600Z 26.4N 75.5W 115 KT 130 MPH 72H 02/0600Z 26.7N 78.3W 120 KT 140 MPH 96H 03/0600Z 26.9N 80.1W 115 KT 130 MPH...INLAND 120H 04/0600Z 28.1N 81.4W 65 KT 75 MPH...INLAND $$ Forecaster Berg
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Hurricane Dorian Forecast Discussion Number 23
2019-08-30 04:56:21| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Thu Aug 29 2019 000 WTNT45 KNHC 300256 TCDAT5 Hurricane Dorian Discussion Number 23 NWS National Hurricane Center Miami FL AL052019 1100 PM AST Thu Aug 29 2019 The NOAA and Air Force Reserve Hurricane Hunter aircraft have been tag-teaming the reconaissance 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. Key Messages: 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 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 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. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 23.3N 68.4W 90 KT 105 MPH 12H 30/1200Z 24.3N 69.4W 100 KT 115 MPH 24H 31/0000Z 25.4N 71.1W 105 KT 120 MPH 36H 31/1200Z 26.0N 73.0W 110 KT 125 MPH 48H 01/0000Z 26.3N 74.7W 115 KT 130 MPH 72H 02/0000Z 26.8N 77.9W 120 KT 140 MPH 96H 03/0000Z 27.0N 79.8W 120 KT 140 MPH 120H 04/0000Z 27.5N 81.0W 65 KT 75 MPH...INLAND $$ Forecaster Blake
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Hurricane Dorian Forecast Discussion Number 22
2019-08-29 22:47:17| National Hurricane Center (Atlantic)
Issued at 500 PM AST Thu Aug 29 2019 000 WTNT45 KNHC 292047 TCDAT5 Hurricane Dorian Discussion Number 22 NWS National Hurricane Center Miami FL AL052019 500 PM AST Thu Aug 29 2019 There has been little overall change in the structure of Dorian today. The hurricane has several well-defined bands of convection wrapping into the center and a small central dense overcast. The small eye has not been as apparent in geostationary satellite imagery this afternoon, but the NOAA Hurricane Hunter aircraft reported concentric eyewall diameters of 4 and 22 n mi several hours ago. The latest satellite intensity estimates still support an initial intensity of 75 kt, which is also in line with the earlier SFMR data from the aircraft. The next reconnaissance aircraft is scheduled to investigate the hurricane this evening. Dorian is moving northwestward or 325 at 11 kt. The hurricane should continue moving northwestward tonight between an upper-level low just to the west of Dorian and a mid-level ridge near Bermuda. On Friday, the ridge is forecast to begin building westward to the north of the cyclone, and this pattern is expected to cause the hurricane to turn west-northwestward. A west-northwestward to westward motion should then continue into the weekend with Dorian moving near or over the northwestern Bahamas and toward the Florida peninsula. The guidance envelope has nudged southward this cycle, with the ECMWF and HMON along the southern side, and the GFS bracketing the northern side. There has also been an increase in along-track spread or speed differences with day 5 positions among the dynamical models ranging from near the northwestern Bahamas to the northeastern Gulf of Mexico. This appears to be the result of differences in the models' depiction of the strength or lack thereof of the western portion of the ridge by day 5. The new NHC track forecast is essentially unchanged through the first 2 to 3 days, but has been adjusted southward and somewhat slower than the previous advisory at 96 and 120 hours. 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. The new intensity forecast is unchanged from the previous one. Dorian will be moving through a favorable environment of low vertical wind shear and warm sea surface temperatures. This should allow for at least steady intensification, and Dorian is forecast to become major hurricane on Friday. Dorian is predicted to remain a dangerous hurricane throughout the remainder of the forecast period. The NHC intensity forecast is again near the upper end of the guidance in best agreement with the HWRF and FSSE models. The National Weather Service has begun 6-hourly upper-air soundings across portions of the mid-Atlantic and southeastern United States. Six-hourly balloons are also being launched in Bermuda and Nassau in the Bahamas. A NOAA G-IV synoptic surveillance mission is ongoing, and the data from this flight will be assimilated into the 0000 UTC model cycle. Key Messages: 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 there tonight or Friday. Residents should have their hurricane plan in place and listen to 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 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. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 22.5N 67.7W 75 KT 85 MPH 12H 30/0600Z 23.8N 68.7W 90 KT 105 MPH 24H 30/1800Z 25.2N 70.4W 100 KT 115 MPH 36H 31/0600Z 26.0N 72.3W 105 KT 120 MPH 48H 31/1800Z 26.5N 74.2W 110 KT 125 MPH 72H 01/1800Z 27.0N 77.7W 115 KT 130 MPH 96H 02/1800Z 27.5N 80.0W 115 KT 130 MPH 120H 03/1800Z 28.1N 81.4W 65 KT 75 MPH...INLAND $$ Forecaster Brown
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Hurricane Dorian Forecast Discussion Number 21
2019-08-29 16:47:42| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Thu Aug 29 2019 000 WTNT45 KNHC 291447 TCDAT5 Hurricane Dorian Discussion Number 21 NWS National Hurricane Center Miami FL AL052019 1100 AM AST Thu Aug 29 2019 The small eye of Dorian has appeared intermittently in infrared satellite imagery this morning. Recent reports from a NOAA P-3 aircraft indicate that there is now a double eyewall structure, with a small inner eye only 5 n mi in diameter and a larger 25-n mi diameter outer eyewall. The minimum pressure has fallen to around 986 mb. The concentric eyewall structure is likely why the aircraft has not found any stronger winds yet in the storm, despite the decrease in central pressure. The initial intensity remains 75 kt for this advisory. Aircraft and satellite fixes show that Dorian is moving northwestward, or 325 degrees at 11 kt. Dorian is forecast to continue moving northwestward during the next 24-36 hours between an upper-level low that will be dropping southwestward across the Florida Straits and a mid-level ridge to the northeast of the hurricane. After that time, a ridge is forecast to build to the north of Dorian, which should cause the track to bend back toward the west-northwest. The track guidance becomes more divergent beyond 72 hours, primarily due to model differences in the strength of the ridge and whether a weakness develops in the ridge late in the period. The new NHC track forecast is virtually unchanged from the previous advisory, and lies very close to the multi-model consensus. It should be noted that the ECMWF, UKMET, and HFIP corrected consensus models remain south of the official forecast. The spread of the deterministic models and the various ensemble guidance is still considerable at days 4 and 5, and it is too soon to specify where along the Florida east coast the greatest impacts could occur. Environmental conditions consisting of warm waters and low vertical wind shear along the path of the hurricane should allow for at least steady intensification during the next 2 to 3 days. With the small inner core and favorable conditions, rapid strengthening also remains a possibility, although not likely in the very short term given the concentric eyewall structure. The updated NHC intensity forecast calls for Dorian to become a major hurricane on Friday, and shows a slightly higher peak intensity than the previous forecast. The official forecast is at the upper end of the guidance, in best agreement with the HCCA and HWRF models. Key Messages: 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 there tonight or Friday. Residents should have their hurricane plan in place and listen to 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 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. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 21.4N 67.2W 75 KT 85 MPH 12H 30/0000Z 22.9N 68.1W 85 KT 100 MPH 24H 30/1200Z 24.5N 69.6W 100 KT 115 MPH 36H 31/0000Z 25.6N 71.4W 105 KT 120 MPH 48H 31/1200Z 26.3N 73.4W 110 KT 125 MPH 72H 01/1200Z 27.0N 76.9W 115 KT 130 MPH 96H 02/1200Z 27.5N 79.8W 115 KT 130 MPH 120H 03/1200Z 28.1N 81.5W 65 KT 75 MPH...INLAND $$ Forecaster Brown
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