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Remnants of Harvey Forecast Discussion Number 11

2017-08-20 04:34:05| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sat Aug 19 2017 000 WTNT44 KNHC 200233 TCDAT4 Remnants Of Harvey Discussion Number 11 NWS National Hurricane Center Miami FL AL092017 1100 PM EDT Sat Aug 19 2017 An Air Force Reserve Hurricane Hunter aircraft investigated Harvey earlier this evening and was unable to close off a center of circulation. The plane found a well-defined wind shift across the wave axis, and winds decreased as the plane flew south along the axis toward a pressure minimum south of 14N. Harvey has therefore degenerated into an open wave, and this will be the last advisory. Maximum surface winds, as measured by the plane, remain 30 kt. As a side note, the associated deep convection has continued to lose organization and is now oriented linearly from northeast to southwest along the wave axis. Harvey's remnants are moving quickly westward with a motion of 275/19 kt. A fast westward to west-northwestward motion is expected to continue for the next couple of days as the wave moves along the southern periphery of the subtropical ridge. A break in the ridge caused by a mid- to upper-level low over the Gulf of Mexico could cause the system to turn northwestward and slow down as it moves across the Yucatan Peninsula and into the Bay of Campeche in 3-5 days. The global models, particularly the GFS and ECMWF, deserve a lot of credit for showing Harvey dissipating, or at least not strengthening, over the Caribbean Sea. Even though the vertical shear that has been plaguing the system is expected to diminish in 24-48 hours, the system's fast motion and ambient dry air will likely keep Harvey's remnants from regenerating into a tropical cyclone in the near term. For that reason, the solutions shown by the GFS, ECMWF, and UKMET appear most reasonable, keeping the system as an open wave, or possibly regenerating to a tropical depression before it reaches Belize and the Yucatan coast. Regeneration is also possible if the remnants emerge over the Bay of Campeche. The remnants of Harvey will be monitored for signs of regeneration and for the possibility of bringing tropical storm conditions to Belize and the Yucatan Peninsula of Mexico during the next couple of days. If necessary, advisories could be resumed and tropical storm watches or warnings issued before Harvey regains tropical cyclone status. Please refer to the Atlantic Tropical Weather Outlook for this system's potential to regenerate into a tropical cyclone, beginning with the 2 AM issuance on Sunday morning. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 14.3N 71.8W 30 KT 35 MPH...REMNANTS OF HARVEY 12H 20/1200Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm Kenneth Forecast Discussion Number 6

2017-08-19 22:35:37| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sat Aug 19 2017 000 WTPZ43 KNHC 192035 TCDEP3 Tropical Storm Kenneth Discussion Number 6 NWS National Hurricane Center Miami FL EP132017 200 PM PDT Sat Aug 19 2017 Kenneth is on a strengthening trend. The cloud pattern of the tropical storm consists of a central dense overcast and curved outer bands, mostly on the south and west portions of the circulation. A partial SSMI/S overpass around 1500 UTC shows a mid-level eye feature, but it also indicated that the system is still vertically tilted from northeast to southwest, likely the result of northeasterly shear. The Dvorak classifications from TAFB/SAB and ADT values from CIMSS at the University of Wisconsin are unanimously 3.5/55 kt, and the initial wind speed is increased to that value. Kenneth is moving west-northwestward at 16 kt on the south side of a narrow mid-level ridge. A decrease in forward speed and a turn to the northwest is expected during the next 2 to 3 days while the storm moves toward the southwestern periphery of the ridge. Thereafter, an even slower motion toward the north-northwest is forecast as Kenneth moves into a break in the ridge caused by a large-scale trough off of the west coast of the United States. The track models have shifted a little to the south and west this cycle, and the NHC forecast has been adjusted in those directions. The environmental conditions appear generally favorable for Kenneth to keep strengthening during the next 36 hours or so, and the system is forecast to become a hurricane as early as tonight. After that time, SSTs fall below 26 deg C along the expected path of Kenneth, and these cool waters combined with a drier air mass should end the strengthening trend and induce gradual weakening. An increase in south-southwesterly shear in 4 to 5 days will also aid in the weakening process. The NHC intensity forecast is higher than the previous one and is in best agreement with the IVCN and HCCA consensus models. This forecast also calls for Kenneth to become a post-tropical cyclone by the end of the period when it will be over SSTs near 22 deg C. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 15.9N 123.8W 55 KT 65 MPH 12H 20/0600Z 16.5N 125.8W 65 KT 75 MPH 24H 20/1800Z 17.2N 127.9W 75 KT 85 MPH 36H 21/0600Z 18.1N 130.0W 80 KT 90 MPH 48H 21/1800Z 19.1N 131.5W 75 KT 85 MPH 72H 22/1800Z 21.8N 133.4W 65 KT 75 MPH 96H 23/1800Z 24.4N 134.7W 45 KT 50 MPH 120H 24/1800Z 27.1N 135.9W 35 KT 40 MPH...POST-TROPICAL $$ Forecaster Cangialosi

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Tropical Depression Harvey Forecast Discussion Number 10

2017-08-19 22:34:37| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Sat Aug 19 2017 000 WTNT44 KNHC 192034 TCDAT4 Tropical Depression Harvey Discussion Number 10 NWS National Hurricane Center Miami FL AL092017 500 PM EDT Sat Aug 19 2017 The cloud pattern of Harvey has continued to decay during the day, at least in part due to 15-20 kt of northerly shear. The convective area near the center is neither very concentrated or curved, and overall the pattern more resembles that of an open wave than a tropical cyclone. Based on the decay and data from the aircraft mission this morning, the cyclone is downgraded to a tropical depression. Another Air Force Reserve Hurricane Hunter aircraft will investigate the system this evening to see if the circulation still exists. The intensity forecast is problematic. The current shear should subside over the next 24 h, and the statistical guidance responds to this by forecasting significant strengthening. On the other hand, the structure of the cyclone has decayed to the point where it may not be able to take advantage of the better environment, as suggested by the ECMWF and GFS. The intensity forecast follows the trend of the previous forecast, albeit with lower intensities, in showing gradual strengthening until landfall in Belize or Yucatan. However, an alternative forecast scenario is that the system degenerates to an open wave and is unable to regenerate during the next 72 h. The initial motion remains 275/19. There is no change in the forecast philosophy from the previous advisory, and there are only minor tweaks to the forecast track. A low- to mid-level ridge extending across the western Atlantic should keep Harvey, or its remnants, on a fast westward course across the Caribbean Sea for the next 36 h. Thereafter, there should be a weakness in the ridge north of Harvey caused by a strong mid/upper-level low currently seen in water vapor imagery over the Gulf of Mexico. This pattern should cause a turn toward the west-northwest and a decrease in forward speed. The track guidance remains in good agreement that Harvey should pass near or just north of northeastern Honduras, and then cross Belize and/or the Yucatan Peninsula into the Bay of Campeche. A Tropical Storm Watch could be required for portions of the northern coast of Honduras and northeastern Nicaragua tonight. At the present time, there is enough uncertainty about whether Harvey will actually be a tropical storm in 48 h that a watch is not warranted. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 14.1N 70.0W 30 KT 35 MPH 12H 20/0600Z 14.3N 73.0W 30 KT 35 MPH 24H 20/1800Z 14.6N 77.0W 35 KT 40 MPH 36H 21/0600Z 15.2N 80.5W 40 KT 45 MPH 48H 21/1800Z 16.0N 83.8W 45 KT 50 MPH 72H 22/1800Z 18.0N 89.0W 45 KT 50 MPH...INLAND 96H 23/1800Z 19.0N 92.0W 30 KT 35 MPH...OVER WATER 120H 24/1800Z 19.5N 94.0W 40 KT 45 MPH $$ Forecaster Beven

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Tropical Storm Harvey Forecast Discussion Number 9

2017-08-19 16:49:59| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sat Aug 19 2017 000 WTNT44 KNHC 191449 TCDAT4 Tropical Storm Harvey Discussion Number 9 NWS National Hurricane Center Miami FL AL092017 1100 AM AST Sat Aug 19 2017 Harvey has become less organized in visible imagery since this time yesterday, with the convective pattern becoming elongated and the circulation looking less well defined. In addition, an Air Force Reserve Hurricane Hunter aircraft could not close the circulation at 850 mb, but was able to close the circulation at 1000 ft. The plane has not yet reported tropical-storm-force winds, but the northwestern quadrant was not well sampled. Thus, the initial intensity is held at a possibly generous 35 kt. The initial motion is now 275/19. A low- to mid-level ridge extending across the western Atlantic should keep Harvey on a fast westward course across the Caribbean Sea for the next 36-48 hours. Thereafter, there should be a weakness in the ridge north of Harvey caused by a strong mid/upper-level low currently seen in water vapor imagery over the Gulf of Mexico. This pattern should cause a turn toward the west-northwest and a decrease in forward speed. The track guidance is in good agreement that Harvey should pass near or just north of northeastern Honduras, and then cross Belize and/or the Yucatan Peninsula into the Bay of Campeche, and based on this the new forecast track follows the guidance with only minor changes from the previous track. The ongoing moderate vertical shear should continue for another 12-24 h or so, and combined with the current lack of organization should allow at best only slow strengthening. After that, the upper-level winds are expected to become favorable for strengthening as the system moves over the deep warm waters of the western Caribbean. The intensity forecast follows the previous forecast in calling for a peak intensity of 60 kt just before the system reaches Belize or the Yucatan Peninsula. Harvey should weaken as it crosses the southern portion of the Yucatan Peninsula between 72-96 h, followed by some re-intensification over the Bay of Campeche. It should be noted that any additional loss of organization in the next 12-24 h would result in the cyclone degenerating into an easterly wave. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 13.9N 68.1W 35 KT 40 MPH 12H 20/0000Z 14.1N 70.9W 35 KT 40 MPH 24H 20/1200Z 14.4N 74.9W 40 KT 45 MPH 36H 21/0000Z 14.9N 78.7W 45 KT 50 MPH 48H 21/1200Z 15.7N 82.4W 50 KT 60 MPH 72H 22/1200Z 17.5N 88.0W 60 KT 70 MPH 96H 23/1200Z 19.0N 91.5W 30 KT 35 MPH 120H 24/1200Z 19.5N 93.5W 40 KT 45 MPH $$ Forecaster Beven

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Tropical Storm Kenneth Forecast Discussion Number 5

2017-08-19 16:46:31| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sat Aug 19 2017 000 WTPZ43 KNHC 191446 TCDEP3 Tropical Storm Kenneth Discussion Number 5 NWS National Hurricane Center Miami FL EP132017 800 AM PDT Sat Aug 19 2017 A couple of recent microwave overpasses has revealed that the center of Kenneth remains near the northeastern edge of the deep convection. Although the upper-level outflow is well established over the southwestern and western portions of the circulation, it is somewhat restricted over the northeastern quadrant due to about 15 kt of shear as diagnosed by a UW-CIMSS shear analysis. Subjective and objective Dvorak T-numbers are around 3.0 (45 kt) from the various agencies, but the initial wind speed is conservatively raised to 40 kt, since I would rather wait to see visible satellite images to get a better handle on Kenneth's structure. Kenneth is moving west-northwestward, 285 degrees, at 14 kt. The tropical storm is moving around the southwestern portion of a low- to mid-level ridge that is located just west of the southern Baja peninsula. Kenneth is expected to reach the western portion of the ridge in about 48 hours, which should cause the cyclone to turn northwestward, then north-northwestward later in the period. The track guidance remains in good agreement through 48 hours, but diverges after that time. The latest run of the GFS has shifted a little westward, but remains along the eastern side of the guidance envelope, with the ECMWF along the western edge. The new NHC track forecast has been nudged westward to be closer to the various consensus aids that have generally shifted in that direction this cycle. The global models predict that the upper-level wind pattern over Kenneth should become more conducive for strengthening over the next day or so. During that time Kenneth will be moving over SSTs of 27 to 28C, which should allow for intensification, and the NHC foreast once again brings Kenneth to hurricane strength on Sunday. After 48 hours, decreasing SSTs should result in gradual weakening. The updated NHC intensity foreast is a little above the statistical guidance and ICON consensus model through 48 hours, but is generally close to the HFIP corrected consensus. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 15.8N 121.8W 40 KT 45 MPH 12H 20/0000Z 16.4N 124.0W 50 KT 60 MPH 24H 20/1200Z 17.0N 126.4W 60 KT 70 MPH 36H 21/0000Z 17.9N 128.6W 65 KT 75 MPH 48H 21/1200Z 18.9N 130.4W 65 KT 75 MPH 72H 22/1200Z 21.5N 132.3W 60 KT 70 MPH 96H 23/1200Z 24.3N 133.4W 45 KT 50 MPH 120H 24/1200Z 27.0N 134.7W 35 KT 40 MPH $$ Forecaster Brown

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