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Tropical Depression Nine Forecast Discussion Number 5

2019-09-13 22:43:27| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Fri Sep 13 2019 000 WTNT44 KNHC 132043 TCDAT4 Tropical Depression Nine Discussion Number 5 NWS National Hurricane Center Miami FL AL092019 500 PM EDT Fri Sep 13 2019 An Air Force plane extensively investigated the disturbance near the Bahamas during the past several hours, and in the last portion of the mission, the crew was able to locate a center of circulation, although weak, near the convection. The center was a little bit to the east of the previous estimates. Satellite images also indicate that the cloud pattern has become a little better organized and Dvorak estimates are T2.0 and 1.5 from TAFB and SAB, respectively. On this basis, the disturbance has been classified as a tropical depression with 25 kt winds. Conditions are not ideal for strengthening since the depression is still embedded within a moderate shear environment, but this parameter is not expected to be strong enough to halt additional development. The NHC forecast still calls for this system to become a tropical storm on Saturday with gradual intensification thereafter. Global models insist on further development, and the reliable guidance suggests that the cyclone could even reach hurricane intensity in about 3 days, and so does the NHC forecast. By then, the system is expected to be over the Atlantic waters well southeast of the coast of the Carolinas. Due to the reformation of the apparent center, the initial motion is highly uncertain. The best estimate is toward the northwest or 305 degrees at 7 kt. A weakness in the ridge over the western Atlantic is forecast to develop, and this pattern should steer the system slowly toward the northwest and then northward. In about 3 days, an eastward moving mid-latitude trough will force the system to recurve away from the coast toward the Atlantic. The track guidance has shifted to the east again, and this shift is larger due to the eastward formation of the center. Consequently, the NHC track forecast was adjusted in that direction, but it remains on the western edge of the guidance envelope. Key Messages: 1. The depression is forecast to become a tropical storm within the next 24 hours and will likely bring tropical-storm-force winds and heavy rainfall to portions of the northwestern Bahamas later today and Saturday. Significant storm surge is not expected in the northwest Bahamas from this system. Residents there should follow any advice given by local officials. 2. The system could still bring tropical storm conditions to portions of the Florida east coast. Residents there should monitor the progress of this system and follow any advice given by local officials. 3. Heavy rainfall and scattered flash flooding is possible this weekend in coastal sections of eastern Florida, Georgia, and South Carolina. The chance of heavy rainfall affecting coastal North Carolina early next week continues to diminish. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 25.6N 75.0W 25 KT 30 MPH 12H 14/0600Z 26.2N 76.0W 30 KT 35 MPH 24H 14/1800Z 27.4N 77.6W 35 KT 40 MPH 36H 15/0600Z 28.8N 78.5W 45 KT 50 MPH 48H 15/1800Z 30.0N 78.8W 55 KT 65 MPH 72H 16/1800Z 31.5N 76.5W 65 KT 75 MPH 96H 17/1800Z 32.0N 73.0W 70 KT 80 MPH 120H 18/1800Z 32.5N 68.0W 75 KT 85 MPH $$ Forecaster Avila

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Potential Tropical Cyclone Nine Forecast Discussion Number 4

2019-09-13 16:55:46| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Fri Sep 13 2019 000 WTNT44 KNHC 131455 TCDAT4 Potential Tropical Cyclone Nine Discussion Number 4 NWS National Hurricane Center Miami FL AL092019 1100 AM EDT Fri Sep 13 2019 Preliminary data from a reconnaissance plane indicate that the disturbance has not developed a well-defined center yet and continues to be characterized by an elongated SW to NE trough of low pressure. Satellite images however, suggest that the system could be consolidating a little bit farther to the east within the area of deep convection. The reconnaissance plane will also check this region soon. In this advisory, the initial position is a point near the middle of of the trough, but not quite as far east as the convective area. The initial intensity remains 25 kt. The disturbance is embedded within a moderate shear environment, but this parameter is not expected to be strong enough to halt development. The NHC forecast still calls for this system to become a tropical cyclone later today or Saturday. Global models develop the system and guidance suggests that the cyclone could even reach hurricane intensity by the end of the forecast period. By then, the system is expected to be over the Atlantic well southeast of the coast of the Carolinas. Due to a lack of a well-defined center, the initial motion is highly uncertain. It appears that there has been little motion during the past few hours. A weakness in the ridge over the western Atlantic is forecast to develop and this pattern should steer the system slowly toward the northwest and then northward. In about 3 days, an eastward moving mid-latitude trough will force the system to recurve away from the coast toward the Atlantic. The guidance has shifted a little to east this morning and consequently the NHC track forecast was adjusted in that direction. However, the official forecast is still on the western edge of the guidance envelope. If the disturbance develops a little more to the east, the track forecast will probably adjusted to the right later today. Key Messages: 1. The system is expected to become a tropical storm and bring tropical-storm-force winds and heavy rainfall to portions of the northwestern Bahamas later today and Saturday. Significant storm surge is not expected in the northwest Bahamas from this system. Residents there should follow any advice given by local officials. 2. The system could bring tropical-storm-force winds to portions of the Florida east coast over the weekend. Residents there should monitor the progress of this system and follow any advice given by local officials. 3. Heavy rainfall and scattered flash flooding is possible this weekend in coastal sections of eastern Florida, Georgia, and South Carolina. Depending on the track of the system, heavy rainfall could reach eastern North Carolina next week. 4. Note that forecast uncertainty for these disturbances is generally larger than for tropical cyclones, especially beyond 48-72 hours. FORECAST POSITIONS AND MAX WINDS INIT 13/1500Z 25.0N 74.5W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 14/0000Z 25.8N 76.5W 30 KT 35 MPH...TROPICAL CYCLONE 24H 14/1200Z 26.6N 78.0W 35 KT 40 MPH 36H 15/0000Z 28.0N 79.4W 40 KT 45 MPH 48H 15/1200Z 29.2N 80.0W 50 KT 60 MPH 72H 16/1200Z 31.0N 79.0W 60 KT 70 MPH 96H 17/1200Z 31.5N 75.0W 65 KT 75 MPH 120H 18/1200Z 32.0N 71.5W 70 KT 80 MPH $$ Forecaster Avila

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Potential Tropical Cyclone Nine Forecast Discussion Number 3

2019-09-13 10:58:17| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Fri Sep 13 2019 000 WTNT44 KNHC 130858 TCDAT4 Potential Tropical Cyclone Nine Discussion Number 3 NWS National Hurricane Center Miami FL AL092019 500 AM EDT Fri Sep 13 2019 Satellite imagery and surface observations indicate that the tropical disturbance is currently comprised of a trough elongated from west-southwest to east-northeast, with a vorticity center near a loosely curved convective band at the eastern end of the trough. While the system has become a little better organized since the last advisory, it does not yet have a well-defined circulation center. The initial intensity remains 25 kt based on satellite intensity estimates and earlier scatterometer data. The disturbance is now moving a little faster, with the initial motion of 315/5. The system is to the south of a low- to mid-level ridge over the southeastern United States, and it is to the east of a mid- to upper-level low over the central Gulf of Mexico. The large-scale models forecast the ridge to shift eastward into the Atlantic during the next 24-48 h, with a weakness developing near the southeastern coast of the United States and the east coast of the Florida peninsula. The track guidance indicates that the disturbance will move generally northwestward for 48 h or so, followed by a turn to the north and eventually to the northeast as the system moves through the weakness in the ridge. There is some spread in the guidance, with the GFS model taking a weaker system into the Florida peninsula while the UKMET and ECMWF models show a stronger cyclone farther offshore. Overall, there has been an eastward shift of the guidance since the previous advisory, especially after 72 h. The new forecast track is thus also nudged a little to the east and now calls for the system to spend less time over the Florida peninsula than previously forecast. The new forecast track is to the left of the center of the guidance envelope and the consensus models, and additional adjustments may be necessary once the circulation center becomes better defined. The disturbance is currently in an environment of moderate southwesterly shear and upper-level divergence caused by the upper-level low and a shortwave trough extending from the low eastward to the southeastern Bahamas. The shear should gradually diminish during the next couple of days, which should allow the disturbance to develop into a tropical cyclone and intensify. The large-scale models forecast the shear to increase after 72 h as a mid-latitude westerly trough moves through the southeastern United States and approaches the system. The new intensity forecast is similar to the previous forecast through 72 h, then it is stronger than the previous forecast due to the forecast track keeping the system more over water. Key Messages: 1. The system is expected to become a tropical storm and bring tropical-storm-force winds and heavy rainfall to portions of the northwestern Bahamas today and Saturday. Significant storm surge is not expected in the northwest Bahamas from this system. Residents there should follow any advice given by local officials. 2. The system could bring tropical-storm-force winds to portions of the Florida east coast over the weekend. Residents there should monitor the progress of this system and follow any advice given by local officials. 3. Heavy rainfall is possible from Potential Tropical Cyclone Nine across portions of eastern Florida into this weekend, which could produce flash flooding. There is greater uncertainty than usual in heavy rainfall prospects farther north across the Carolinas. 4. Note that forecast uncertainty for these disturbances is generally larger than for tropical cyclones, especially beyond 48-72 hours. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 24.6N 75.2W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 13/1800Z 25.1N 76.2W 30 KT 35 MPH...TROPICAL DEPRESSION 24H 14/0600Z 26.0N 77.8W 35 KT 40 MPH 36H 14/1800Z 27.0N 79.3W 40 KT 45 MPH 48H 15/0600Z 28.2N 80.4W 45 KT 50 MPH 72H 16/0600Z 30.3N 81.1W 50 KT 60 MPH 96H 17/0600Z 31.0N 80.5W 50 KT 60 MPH 120H 18/0600Z 32.0N 78.5W 55 KT 65 MPH $$ Forecaster Beven

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Tropical Storm Kiko Forecast Discussion Number 4

2019-09-13 10:52:19| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Fri Sep 13 2019 000 WTPZ43 KNHC 130852 TCDEP3 Tropical Storm Kiko Discussion Number 4 NWS National Hurricane Center Miami FL EP132019 300 AM MDT Fri Sep 13 2019 Kiko's convective pattern has still not gotten any better organized. There's a small patch of convection near the estimated center, with another larger cluster much farther south. For the most part, however, the circulation consists of a broken low- and mid-level cloud deck with a few embedded showers. Subjective Dvorak estimates from TAFB and SAB are T2.0/30 kt, while objective numbers are only slightly higher. The initial intensity is being held at 35 kt, but it's entirely possible that Kiko may not be producing tropical-storm-force winds at this time. The GOES-17 air mass product shows that Kiko is surrounded by some of the driest air over the entire tropical eastern Pacific, which could be contributing to the system's convective struggles. And going forward, it appears that the thermodynamic environment could be less than ideal for significant strengthening, with SHIPS model diagnostics showing environmental stability to be the biggest negative factor. That being said, vertical shear is expected to be less than 10 kt for at least the next 3 days, so strengthening is likely if the dry air can be mixed out of the circulation. The new NHC forecast continues to show Kiko reaching hurricane strength in about 48 hours, although the peak intensity has been tempered a bit based on the latest guidance. The official forecast is close to a blend of the Florida State Superensemble and the HFIP Corrected Consensus aids. Kiko is moving west-northwestward, or 295/9 kt, to the south of a mid-level ridge which extends along the U.S./Mexico border. This motion should continue for the next 3 days, and the track models are in good agreement on this solution. After day 3, there is a bifurcation of the models, with the GFS, HMON, COAMPS-TC, and Canadian turning Kiko northwestward or northward into a break in the ridge, and the ECMWF, UKMET, HWRF, and the consensus aids maintaining a west-northwestward or even westward heading on days 4 and 5. Due to this divergence, the updated forecast shows a slightly slower motion toward the end of the forecast period, but the track itself is very similar to the previous forecast, lying near the northern boundary of the southern camp of models. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 16.8N 113.5W 35 KT 40 MPH 12H 13/1800Z 17.1N 114.9W 40 KT 45 MPH 24H 14/0600Z 17.5N 116.6W 50 KT 60 MPH 36H 14/1800Z 17.9N 118.3W 60 KT 70 MPH 48H 15/0600Z 18.4N 120.0W 65 KT 75 MPH 72H 16/0600Z 19.4N 123.1W 65 KT 75 MPH 96H 17/0600Z 20.5N 125.5W 45 KT 50 MPH 120H 18/0600Z 21.0N 127.5W 35 KT 40 MPH $$ Forecaster Berg

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Potential Tropical Cyclone Nine Forecast Discussion Number 2

2019-09-13 04:57:14| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Thu Sep 12 2019 000 WTNT44 KNHC 130257 TCDAT4 Potential Tropical Cyclone Nine Discussion Number 2 NWS National Hurricane Center Miami FL AL092019 1100 PM EDT Thu Sep 12 2019 An Air Force Reserve reconnaissance aircraft earlier this afternoon found a closed but very broad cyclonic circulation along with 1000-ft flight-level and SFMR surface winds that supported an intensity of 25 kt. Recent ship reports also support an intensity of 25 kt, although stronger winds could be present in some of the fragmented convective bands located in the northeastern quadrant. The initial motion is an uncertain 310/02 kt. The disturbance has been meandering over the southeastern Bahamas the past several hours due to southwesterly mid-/upper-level winds associated with an east-west oriented shortwave trough impinging on the west side of the circulation. A large upper-low located over the central Gulf of Mexico that has produced this shortwave trough is expected to spin out another trough on Friday that will move across South Florida and the Straits, impinging on the disturbance and hindering any significant northwestward motion. By late Friday and Saturday, however, the upper-level is expected to have moved into the western Gulf of Mexico, ending any negative effects in the disturbance. This expected to result in the formation of a tropical cyclone with a deeper vortex column that should get steered basically northwestward in combined deep-layer southeasterly flow between the upper-low to the west and a ridge to the northeast. The new NHC track forecast is basically just an extension of the previous forecast track, albeit a little slower, and lies down the middle of the widely divergent guidance envelope, close to the various simple consensus models, and to the right of the NOAA-HCCA consensus model. The aforementioned complex steering flow pattern will also play a major role in the intensification process. The two shortwaves troughs are expected to hinder significant convective organization for the next 24-30 hours due to their localized increase in the vertical shear and intrusions of dry air. By 36 hours and beyond, however, those negative factors are forecast to abate, resulting in the disturbance moving underneath an axis of strong upper-level difluence and speed divergence near or just to the east of the Florida east coast. This more favorable upper-level outflow regime should allow for convection to develop and organize fairly quickly around the center before the system reaches the Florida east coast, which should result in the formation of a moderate tropical storm. Although the center is forecast to be inland at 72-96 hours, the center is expected be close enough to the coast to keep tropical-storm-force ongoing over the coastal waters through 120 hours. The official intensity forecast is identical to the previous advisory and follows a blend of the consensus models HCCA and IVCN. Key Messages: 1. The disturbance is expected to become a tropical storm and bring tropical storm force winds to portions of the northwest Bahamas within 36 hours. Note that forecast uncertainty for these disturbances is generally larger than for tropical cyclones, especially beyond 48-72 hours. 2. The system is expected to bring tropical-storm-force winds and heavy rainfall to portions of the northwest Bahamas on Friday and Saturday. Significant storm surge is not expected in the northwest Bahamas from this system. Residents there should follow any advice given by local officials. 3. The system could bring tropical-storm-force winds and rainfall to portions of the Florida east coast over the weekend. Residents there should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 23.8N 74.5W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 13/1200Z 24.6N 75.6W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 24H 14/0000Z 25.5N 77.2W 30 KT 35 MPH...TROPICAL CYCLONE 36H 14/1200Z 26.5N 78.8W 40 KT 45 MPH 48H 15/0000Z 27.5N 80.2W 45 KT 50 MPH 72H 16/0000Z 29.8N 81.8W 40 KT 45 MPH...INLAND 96H 17/0000Z 30.8N 81.4W 40 KT 45 MPH...INLAND 120H 18/0000Z 31.8N 79.8W 45 KT 50 MPH...OVER WATER $$ Forecaster Stewart

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