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Tropical Storm Vicente Forecast Discussion Number 4

2018-10-20 10:37:06| National Hurricane Center (East Pacific)

Issued at 400 AM CDT Sat Oct 20 2018 000 WTPZ43 KNHC 200836 TCDEP3 Tropical Storm Vicente Discussion Number 4 NWS National Hurricane Center Miami FL EP232018 400 AM CDT Sat Oct 20 2018 Radar data from Guatemala indicate that Vicente remains a very small but well-defined tropical cyclone, which has occasionally exhibited an eye-like feature. However, convection has waned during the past few hours, so it is difficult to accurately ascertain the intensity of such a tiny storm since small systems like this can spin up and spin down very quickly owing to minor convective fluctuations. For now, it is assumed that Vicente is still a tropical storm based on satellite intensity estimates of T2.5/35 kt from TAFB and SAB, and 41 kt from UW-CIMSS SATCON; the most recent ADT value, however, was T2.2/32 kt. The initial motion estimate is 290/06 kt. Over the last 18 hours, it appears that Vicente's track has been doing some coastal hugging. That being said, the tropical storm is expected to turn more westward during the next 12 h and emerge over the open Gulf of Tehuantepec where a modest gap wind event is forecast to turn the cyclone southwestward by this evening. The latest 00Z model guidance is surprisingly in very good agreement on the development of this unusual track scenario. By 36-48 hours, a gradual turn toward the west is expected, followed by a motion toward the northwest on days 3-5 as the small cyclone rounds the southwestern periphery of a deep-layer ridge located over the Gulf of Mexico and central Mexico. Assuming Vicente survives the next 96 hours, on day 5 the tropical cyclone is expected to come under the influence of the new and much larger Tropical Depression 24-E -- currently located about 700 nmi to the west -- and possibly become absorbed or forced inland over southwestern Mexico by that system. The new NHC forecast was nudged a little to the west at most forecast times, closer to the HCCA and FSSE corrected consensus models. Vertical shear is forecast to be less than 10 kt and the mid-level moisture is expected to be high with humidity values of more than 75 percent for the next 36 hours. This should allow for some gradual strengthening to occur during that time despite Vicente's proximity to land. By 48 hours and beyond, however, northerly shear is expected to increase across the small cyclone, which should act to cap the intensification process and induce some gradual weakening by 96h. On day 5, the shear is forecast to exceed 20 kt, due in large part to the expected strong outflow from a strengthening TD-24E, resulting in significant weakening or even dissipation of Vicente. The official intensity forecast is similar to but slightly below the previous forecast, and lies close to an average of the HCCA, FSSE, and IVCN consensus models. Vicente should begin to slowly pull away from the coast overnight and on Saturday, however, heavy rainfall, with possible life-threatening flash flooding, is expected over portions southeastern Mexico during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 14.0N 93.1W 35 KT 40 MPH 12H 20/1800Z 14.1N 93.9W 35 KT 40 MPH 24H 21/0600Z 13.5N 95.3W 40 KT 45 MPH 36H 21/1800Z 12.9N 97.1W 40 KT 45 MPH 48H 22/0600Z 13.1N 98.7W 45 KT 50 MPH 72H 23/0600Z 15.2N 101.9W 50 KT 60 MPH 96H 24/0600Z 18.3N 104.9W 50 KT 60 MPH 120H 25/0600Z 21.8N 108.3W 35 KT 40 MPH $$ Forecaster Stewart

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Tropical Storm Vicente Forecast Discussion Number 3

2018-10-20 04:36:33| National Hurricane Center (East Pacific)

Issued at 1000 PM CDT Fri Oct 19 2018 000 WTPZ43 KNHC 200236 TCDEP3 Tropical Storm Vicente Discussion Number 3 NWS National Hurricane Center Miami FL EP232018 1000 PM CDT Fri Oct 19 2018 Radar imagery from Guatemala has been extremely helpful in tracking the center of Vicente, especially after sunset. The low-level center of the small tropical storm appears to have accelerated northwestward during the past couple of hours, away from its rapidly decaying central dense overcast, and is now almost entirely exposed. Analysis from UW-CIMSS indicates that 10-15 knots of northwesterly shear is currently affecting Vicente, and this appears to have been enough to significantly disrupt the organization of the cyclone, probably due to its small size. The initial intensity has been held at 35 kt based on objective and subjective satellite estimates at 00Z, but given the tiny size of Vicente and its large swings in organization since early this morning, its unclear how representative these estimates are of the true maximum winds. Vicente is now moving west-northwestward, or 300/3 kt, and all of the guidance indicates that it will turn westward overnight. After that time, a Gulf of Tehuantepec gap wind event will likely cause the cyclone to turn southwestward, especially if Vicente remains weak and shallow. A few models even indicate the tropical storm could dissipate entirely as it interacts with these winds. Assuming the cyclone makes it past the Gulf of Tehuantepec intact, Vicente should turn back toward the west-northwest or northwest after about 48 h as it gets steered by the flow between a mid-level ridge over Mexico and another tropical cyclone that will likely develop off the coast of Mexico by that time. The NHC forecast has been shifted a little to the west at most forecast times, closer to the HCCA and FSSE aids, but is generally similar to the previous advisory. Due in part to the rapid decline in Vicente's organization this evening, the intensity forecast has been adjusted lower at most forecast hours for the first 48 h of the forecast, but is still generally higher than the model consensus. Most of the intensity guidance still calls for intensification, especially between 36 h and 72 h, when Vicente should be past the Gulf of Tehuantepec, and the shear should remain generally low. By the end of the forecast period, the global models indicate that Vicente will interact with a much larger tropical cyclone to its west, which should cause Vicente to weaken and possibly dissipate, though a 120 h point is still carried in this forecast for continuity purposes. Vicente should begin to slowly pull away from the coast overnight and on Saturday, however, heavy rainfall, with possible life-threatening flash flooding, is expected over portions of El Salvador, Guatemala, and southeastern Mexico during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 13.7N 92.5W 35 KT 40 MPH 12H 20/1200Z 13.7N 93.3W 40 KT 45 MPH 24H 21/0000Z 13.3N 94.3W 45 KT 50 MPH 36H 21/1200Z 12.5N 95.7W 45 KT 50 MPH 48H 22/0000Z 12.3N 97.4W 45 KT 50 MPH 72H 23/0000Z 13.8N 100.8W 55 KT 65 MPH 96H 24/0000Z 17.0N 104.0W 50 KT 60 MPH 120H 25/0000Z 20.5N 107.5W 40 KT 45 MPH $$ Forecaster Zelinsky

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Tropical Storm Vicente Forecast Discussion Number 2

2018-10-19 22:37:00| National Hurricane Center (East Pacific)

Issued at 400 PM CDT Fri Oct 19 2018 000 WTPZ43 KNHC 192036 TCDEP3 Tropical Storm Vicente Discussion Number 2 NWS National Hurricane Center Miami FL EP232018 400 PM CDT Fri Oct 19 2018 Although tiny, the cyclone continues to display well-defined convective banding. The system's quick formation and small size make it difficult to have high confidence in its current intensity, and the various subjective and objective estimates range from T1.8/28 kt from the ADT to T3.0/45 kt from SAB. As a compromise, the intensity is set at 35 kt, which is closest to the TAFB estimate and the most recent SATCON number, and the depression is upgraded to Tropical Storm Vicente. As noted this morning, warm waters and low shear should induce further strengthening during the next 48 hours. On one hand, this intensification could be more than what is being indicated by the models, since small systems can have a tendency to gain strength quickly. On the other hand, Vicente will be interacting with a Gulf of Tehuantepec gap wind event during the next 48 hours, and the storm could end up ingesting some drier, more stable air into its circulation. The NHC intensity forecast favors the former scenario and is a little above the guidance envelope for the first 2-3 days. After day 3, an increase in shear, interaction with another possible tropical cyclone to the west, and possible interaction with land could all conspire to arrest the intensification trend, and weakening is expected by the end of the forecast period. It is also possible that Vicente could dissipate before the end of the 5-day period. This scenario is reminiscent of, and has similarities to, the interaction of Tropical Storm Ileana and Hurricane John back in early August. Vicente is moving very slowly northwestward, or 305/2 kt. The track models are indicating that the ongoing gap winds over the Gulf of Tehuantepec may have a greater influence of Vicente than previously thought, forcing the storm to turn west-southwestward in the next 24-48 hours. After 48 hours, Vicente should gradually enter the flow between mid-level ridging over Mexico and low pressure west of Mexico, causing it to turn back to the west and northwest on days 3 through 5. The new NHC track forecast is not too different from the morning forecast during that period, and it's closest to the paths shown by the GFS, HCCA, and FSSE guidance, which would bring the center close to the coast of Mexico later in the forecast period. There are considerable speed differences, however, and the NHC forecast splits the difference between the fast ECMWF solution and the slow GFS scenario. Even though Vicente should begin to slowly pull away from the coast tonight and on Saturday, heavy rainfall, with possible life-threatening flash flooding, is expected over portions of El Salvador, Guatemala, and southeastern Mexico during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 13.3N 92.2W 35 KT 40 MPH 12H 20/0600Z 13.6N 93.3W 45 KT 50 MPH 24H 20/1800Z 13.3N 94.2W 50 KT 60 MPH 36H 21/0600Z 12.9N 95.2W 55 KT 65 MPH 48H 21/1800Z 12.7N 96.5W 55 KT 65 MPH 72H 22/1800Z 13.7N 99.8W 55 KT 65 MPH 96H 23/1800Z 16.5N 103.0W 55 KT 65 MPH 120H 24/1800Z 20.0N 106.0W 45 KT 50 MPH $$ Forecaster Berg

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Tropical Depression Twenty-three-E Forecast Discussion Number 1

2018-10-19 16:57:24| National Hurricane Center (East Pacific)

Issued at 1000 AM CDT Fri Oct 19 2018 000 WTPZ43 KNHC 191457 TCDEP3 Tropical Depression Twenty-Three-E Discussion Number 1 NWS National Hurricane Center Miami FL EP232018 1000 AM CDT Fri Oct 19 2018 Two distinct areas of low pressure formed late yesterday within a sprawling area of disturbed weather that stretched from Central America westward over the eastern Pacific waters south of Mexico. The easternmost low south of Guatemala is small and has spun up quickly, with deep convection continuing to burst near the center of circulation. Microwave data, first-light visible images, and valuable radar data from Guatemala also show a tight core and increasing convective bands. Maximum winds are set at 30 kt, slightly above last evening's ASCAT pass and a T1.5 Dvorak classification from TAFB, given the system's well-developed structure. The depression is located over warm waters (28-29 degrees Celsius) and in a light-shear environment. These conditions should support further strengthening, and the depression's small size may allow for intensification higher than what is indicated by the intensity models. For this first advisory, the NHC intensity forecast is near the top end of the guidance envelope and levels off the maximum winds in 3-5 days when there could be an increase in shear. Since the low formed recently, the depression's current motion is uncertain. However, microwave fixes indicate that it hasn't moved much since last evening, and the initial motion estimate is slowly west-northwestward, or 300/2 kt. A strong mid-level ridge spanning across the Gulf of Mexico and northern Mexico should steer the cyclone generally westward for the next 3 days or so. After day 3, the ridge is expected to retreat eastward a bit, and the cyclone should begin to turn northwestward between the ridge and another low pressure system to the west. The track models are in good agreement on this general scenario, but there is not agreement on how close the system could get to the coast of Mexico during the forecast period. Therefore, interests along the southern and southwestern coast of Mexico should monitor the progress of this system during the next few days. Regardless of how close it gets to the coast, heavy rainfall, with possible life-threatening flash flooding, is expected over portions of El Salvador, Guatemala, and southeastern Mexico during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 13.3N 91.9W 30 KT 35 MPH 12H 20/0000Z 13.7N 93.2W 35 KT 40 MPH 24H 20/1200Z 13.5N 94.2W 40 KT 45 MPH 36H 21/0000Z 13.3N 94.9W 45 KT 50 MPH 48H 21/1200Z 13.3N 96.1W 50 KT 60 MPH 72H 22/1200Z 13.8N 99.5W 50 KT 60 MPH 96H 23/1200Z 16.0N 103.0W 55 KT 65 MPH 120H 24/1200Z 19.0N 105.5W 55 KT 65 MPH $$ Forecaster Berg

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Remnants of Tara Forecast Discussion Number 11

2018-10-17 04:33:54| Tropical Depression LIDIA

Issued at 1000 PM CDT Tue Oct 16 2018

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