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Hurricane Dorian Forecast Discussion Number 33

2019-09-01 16:57:24| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sun Sep 01 2019 000 WTNT45 KNHC 011457 TCDAT5 Hurricane Dorian Discussion Number 33 NWS National Hurricane Center Miami FL AL052019 1100 AM EDT Sun Sep 01 2019 Air Force and NOAA reconnaissance planes penetrated the distinct eye of Dorian, and found that the hurricane has become extremely intense with a stadium effect in the eye. The NOAA plane reported a peak flight-level wind of 159 kt, while the SFMR from both planes have measured winds between 155 and 170 kt. A dropsonde from the NOAA plane measured a wind gust of 176 kt at the surface. A blend of these measurements yield to an initial intensity of 155 kt, making Dorian the strongest hurricane on record in the northwestern Bahamas. For the next few days, Dorian should experience some fluctuations in intensity, and in addition to eyewall replacement cyclone, the interaction with the northwestern Bahamas should weaken the hurricane slightly. After 3 days, as Dorian moves northward along or offshore of southeast United States coast, the shear is forecast to increase, resulting in a more distinct gradual weakening. Reconnaissance plane and satellite fixes indicate that Dorian, as anticipated, has slowed down and is moving toward the west or 270 degrees at 6 kt. The steering currents are collapsing and Dorian is expected to slow down even more, prolonging its catastrophic effects in the northwestern Bahamas. The NHC forecast calls for a slow west to west-northwest motion during the next 48 hours, with a turn to the north and an increase in forward speed as the mid-level trough along the eastern United States deepens and becomes the dominant steering feature. The current forecast is only a few miles west of the previous one and is basically on top of the multi-model consensus. Both the deterministic and consensus tracks have shown the usual variability to the right or to the left from run to run, but the overall trend is for the hurricane to turn northward offshore but very close to the Florida peninsula. Given the uncertainty in the track forecast and the anticipated increase in size of the hurricane, a Hurricane Watch and Storm Surge Watch have been issued for a portion of the east Florida coast. It is emphasized that although the official track forecast does not show landfall, users should not focus on the exact track. A small deviation to the left of the track could bring the intense core of the hurricane its dangerous winds closer to or onto the coast. Key Messages: 1. A prolonged period of catastrophic winds and storm surge will affect the Abaco Islands today. Everyone there should take immediate shelter and not venture into the eye. These catastrophic conditions are likely on Grand Bahama Island later today or tonight, and efforts to protect life and property there should be rushed to completion. 2. Storm surge and hurricane watches and tropical storm warnings are in effect for portions of the Florida east coast. Life-threatening storm surge and dangerous hurricane-force winds are possible along portions of the Florida east coast through mid-week, as only a slight deviation to the left of the official forecast would bring the core of Dorian near or over the coast. Residents should listen to advice given by local emergency officials. 3. There is an increasing likelihood of strong winds and dangerous storm surge along the coasts of Georgia, South Carolina, and North Carolina later this week. Residents in these areas should continue to monitor the progress of Dorian. 4. Heavy rains, capable of producing life-threatening flash floods, are possible over northern portions of the Bahamas and coastal sections of the southeast and lower mid-Atlantic regions of the United States through late this week. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 26.5N 76.8W 155 KT 180 MPH 12H 02/0000Z 26.6N 77.7W 150 KT 175 MPH 24H 02/1200Z 26.8N 78.5W 145 KT 165 MPH 36H 03/0000Z 27.0N 79.0W 135 KT 155 MPH 48H 03/1200Z 27.4N 79.4W 120 KT 140 MPH 72H 04/1200Z 29.7N 80.2W 100 KT 115 MPH 96H 05/1200Z 32.5N 79.0W 85 KT 100 MPH 120H 06/1200Z 35.5N 74.5W 80 KT 90 MPH $$ Forecaster Avila

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Tropical Storm Juliette Forecast Discussion Number 2

2019-09-01 16:41:24| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Sun Sep 01 2019 000 WTPZ41 KNHC 011441 TCDEP1 Tropical Storm Juliette Discussion Number 2 NWS National Hurricane Center Miami FL EP112019 900 AM MDT Sun Sep 01 2019 Juliette has been quickly organizing this morning. Satellite and microwave data indicate that a small central dense overcast has formed, with a large band on the east side. The current wind speed is set to 50 kt, in line with the recent CIMSS objective Dvorak estimate since the subjective estimates are still catching up with this storm. There's been a significant change to the intensity and size forecasts of Juliette this morning, with guidance now showing a stronger and larger hurricane in about a day. This is consistent with the recent development of the early stages of an inner core, which would allow Juliette to continue to intensify at a fast pace. Indeed, rapid intensification is a distinct possibility due to an environment of low shear and very warm water, and the various rapid intensification indices are all showing this chance. Thus the forecast is raised from the last one, similar to the corrected consensus guidance, and further upward adjustments might be required this afternoon. Fixes show that the storm is moving faster to the northwest this morning. A ridge to the northeast of Juliette should steer the storm on this general path for the next several days, followed by a slight turn toward the west-northwest at the end. Model guidance is in fairly good agreement on this scenario, and the new forecast is basically an update of the previous one, close to the eastern Pacific model consensus TVCE. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 14.3N 108.8W 50 KT 60 MPH 12H 02/0000Z 15.3N 110.3W 60 KT 70 MPH 24H 02/1200Z 16.5N 112.3W 75 KT 85 MPH 36H 03/0000Z 17.4N 114.1W 85 KT 100 MPH 48H 03/1200Z 18.1N 115.6W 90 KT 105 MPH 72H 04/1200Z 19.2N 118.5W 75 KT 85 MPH 96H 05/1200Z 20.5N 121.8W 70 KT 80 MPH 120H 06/1200Z 22.5N 125.5W 60 KT 70 MPH $$ Forecaster Blake

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Hurricane Dorian Forecast Discussion Number 32

2019-09-01 10:59:23| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sun Sep 01 2019 000 WTNT45 KNHC 010859 TCDAT5 Hurricane Dorian Discussion Number 32 NWS National Hurricane Center Miami FL AL052019 500 AM EDT Sun Sep 01 2019 Dorian continues to exhibit a well-defined eye surrounded by very cold cloud tops on satellite images. Observations from an Air Force Hurricane Hunter aircraft from several hours ago indicated that the intensity was still near 130 kt, and since the cloud pattern remains very impressive, it is assumed that Dorian has at least maintained that strength through the present time. The hurricane will remain in a fairly low-shear environment for the next few days, however since it is forecast to move quite slowly over the shallow waters of the northwesternnmost Bahamas through Monday, this would likely result in less available oceanic heat content. Therefore, a very slow weakening is anticipated to commence after 12 hours or so. The official intensity forecast is near the high end of the numerical guidance suite. The hurricane continues moving westward, or about 280/7 kt. A high pressure ridge to the north of Dorian should maintain this westward movement through today. By tonight, the global models show the ridge weakening, and this evolution should result in a slowing of the forward speed, with the hurricane becoming nearly stationary around 48 hours. In comparison to its earlier runs, the new ECMWF track forecast takes the system farther to the west during the next couple of days, and is the southwesternmost model through 48 hours. As a result, the official track forecast has been shifted a little west during that time frame. In 2 to 4 days, Dorian should turn northward in response to a trough over the eastern United States. By the end of the period, the flow on the south side of the trough should cause the cyclone to move northeastward near the Carolinas. The westward shift of the NHC track within the first 48 hours necessitates the change from a Tropical Storm Watch to a Tropical Storm Warning for a portion of the Florida east coast. Although the official track forecast does not show landfall, users should not focus on the exact track since a Florida landfall is still a distinct possibility. Key Messages: 1. A prolonged period of life-threatening storm surge, devastating hurricane-force winds, and heavy rains capable of producing life-threatening flash floods are expected on the Abaco Islands and Grand Bahama through Monday, and a hurricane warning is in effect for these areas. 2. A tropical storm warning is now in effect for a portion of the Florida east coast. Since Dorian is forecast to slow down and turn northward as it approaches the coast, life-threatening storm surge and dangerous hurricane-force winds are still possible along portions of the Florida east coast by the middle part of this week. 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. There is an increasing risk of strong winds and dangerous storm surge along the coasts of Georgia, South Carolina, and North Carolina later this week. Residents in these areas should continue to monitor the progress of Dorian. 4. Heavy rains, capable of producing life-threatening flash floods, are possible over coastal sections of the southeast and lower mid-Atlantic regions of the United States through late this week. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 26.4N 76.0W 130 KT 150 MPH 12H 01/1800Z 26.6N 77.1W 135 KT 155 MPH 24H 02/0600Z 26.7N 78.1W 125 KT 145 MPH 36H 02/1800Z 26.9N 78.7W 120 KT 140 MPH 48H 03/0600Z 27.0N 79.0W 120 KT 140 MPH 72H 04/0600Z 28.9N 79.8W 100 KT 115 MPH 96H 05/0600Z 31.8N 79.6W 85 KT 100 MPH 120H 06/0600Z 34.5N 76.0W 80 KT 90 MPH $$ Forecaster Pasch

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Tropical Storm Juliette Forecast Discussion Number 1

2019-09-01 10:32:19| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Sun Sep 01 2019 000 WTPZ41 KNHC 010832 TCDEP1 Tropical Storm Juliette Discussion Number 1 NWS National Hurricane Center Miami FL EP112019 300 AM MDT Sun Sep 01 2019 Earlier scatterometer surface wind data around 0400 UTC indicate that the low pressure system located about 400 nmi south-southwest of Manzanillo, Mexico, had become better defined and that tropical-storm-force winds were occurring in the northern semicircle. More specifically, an ASCAT-A pass revealed peak surface winds of 42 kt, which could have been slightly rain inflated, and an ASCAT-C pass showed peak winds of 39 kt. Based on a blend of these wind data, the low has been upgraded to a 40-kt tropical storm, the tenth tropical storm of the 2019 eastern North Pacific hurricane season. Juliette's initial motion estimate is an uncertain 310/06 kt. The advisory position is an average of the locations of the mid- and low-level circulation centers, in anticipation of the low-level center noted in the ASCAT-C wind data developing closer to the recent bursts of central deep convection. Otherwise, the track forecast is pretty straight-forward with the NHC model guidance in good agreement on maintaining the deep-layer ridge to the north of Juliette throughout the forecast period. This steering pattern should result in the cyclone moving slowly northwestward today, followed by a turn toward the west-northwest with an increase in forward speed on Monday, with a west-northwestward motion continuing through 120 hours. The NHC forecast track lies close to the tightly packed consensus models HCCA and TVCE. Juliette is expected to remain within a favorable environment for intensification to occur over the next 48-72 hours or so, which is characterized by low vertical wind shear of less than 10 kt, a moist mid-level environment, and sea-surface temperatures (SST) of 28-29 deg C. Therefore, the official intensity forecast calls for steady strengthening, with Juliette expected to become a hurricane on Monday. By 96 hours, the cyclone will be moving over SSTs around 26 deg C and cooler, which should induce gradual weakening. The NHC intensity forecast is above the consensus intensity models HCCA and IVCN, and is close to a blend of the statistical SHIPS intensity models and the dynamical HWRF model. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 13.2N 107.6W 40 KT 45 MPH 12H 01/1800Z 14.5N 109.4W 45 KT 50 MPH 24H 02/0600Z 15.7N 111.5W 55 KT 65 MPH 36H 02/1800Z 16.7N 113.5W 65 KT 75 MPH 48H 03/0600Z 17.6N 115.2W 75 KT 85 MPH 72H 04/0600Z 18.9N 118.0W 75 KT 85 MPH 96H 05/0600Z 20.0N 121.0W 70 KT 80 MPH 120H 06/0600Z 21.8N 124.8W 55 KT 65 MPH $$ Forecaster Stewart

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Hurricane Dorian Forecast Discussion Number 31

2019-09-01 04:56:17| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sat Aug 31 2019 000 WTNT45 KNHC 010256 TCDAT5 Hurricane Dorian Discussion Number 31 NWS National Hurricane Center Miami FL AL052019 1100 PM EDT Sat Aug 31 2019 Data from both Air Force and NOAA Hurricane Hunter aircraft indicate that Dorian remains a very powerful hurricane, and the satellite presentation is still quite impressive with a very stable, well-defined eye. There has been no evidence of concentric eyewalls in aircraft or microwave data, which is somewhat surprising given that the intensity has been at category 4 strength for 24 hours. Both aircraft measured peak flight-level winds that support an initial intensity of 130 kt. There have been some higher surface wind estimates from the SFMR, but these data are questionable based on our experience of very high SFMR-measured wind speeds in recent strong hurricanes that didn't match standard flight-level wind reductions. Dorian is forecast to continue moving over very warm waters and into a low-shear environment during the next 12-24 hours, so some additional strengthening is possible. Difficult-to-predict eyewall cycles, however, are likely to begin at some point within the next day or so and could cause fluctuations in intensity. After 72 hours, increasing southerly shear is likely to produce gradual weakening, but Dorian is foreast to remain a dangerous hurricane through the forecast period. The hurricane is moving westward or 280/7 kt. A high pressure ridge to the north of Dorian is predicted to remain intact into early Sunday, and the hurricane should continue westward. By late Sunday, the dynamical models erode the western portion of the ridge, which should cause the hurricane to slow down and become nearly stationary over the northwestern Bahamas in 36 to 48 hours. After that time, the weakness in the ridge becomes more pronounced, and Dorian is expected to turn northwestward, and eventually northeastward near the southeastern United States coast. Although there is general agreement on this overall scenario, there is still considerable spread on how close the storm will track to the east coast of Florida and the southeastern coast of the United States. The latest HWRF run has shifted westward and takes Dorian across the coast of central Florida. The 18Z GFS also shifted a little left closer to the Florida coast. The latest multi-model consensus aids shifted west closer to the previous NHC track, so very little change to that forecast was made. Although the exact NHC track forecast lies east of the Florida peninsula, a track closer to the coast or even a landfall remain a possibility. Since the updated track was slightly slower than the previous advisory, no additional watches are needed for Florida at this time. Key Messages: 1. A prolonged period of life-threatening storm surge, devastating hurricane-force winds, and heavy rains capable of life-threatening flash floods are expected on the Abaco Islands and Grand Bahama Sunday through Monday, and a hurricane warning is in effect for these areas. 2. A tropical storm watch is in effect for a portion of the Florida east coast. Since Dorian is forecast to slow down and turn northward as it approaches the coast, life-threatening storm surge and dangerous hurricane-force winds are still possible along portions of the Florida east coast by the early to middle part of next week. 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. There is an increasing risk of strong winds and dangerous storm surge along the coasts of Georgia, South Carolina, and North Carolina during the middle of next week. Residents in these areas should continue to monitor the progress of Dorian. 4. Heavy rains, capable of life-threatening flash floods, are possible over coastal sections of the southeastern United States from Monday through Thursday. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 26.3N 75.1W 130 KT 150 MPH 12H 01/1200Z 26.4N 76.3W 135 KT 155 MPH 24H 02/0000Z 26.6N 77.4W 130 KT 150 MPH 36H 02/1200Z 26.8N 78.1W 125 KT 145 MPH 48H 03/0000Z 27.0N 78.5W 120 KT 140 MPH 72H 04/0000Z 28.5N 79.3W 110 KT 125 MPH 96H 05/0000Z 31.1N 80.0W 95 KT 110 MPH 120H 06/0000Z 34.0N 77.0W 85 KT 100 MPH $$ Forecaster Brown

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