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Tropical Storm VANCE Forecast Discussion Number 8

2014-11-01 03:36:21| National Hurricane Center (East Pacific)

Issued at 800 PM PDT FRI OCT 31 2014 000 WTPZ41 KNHC 010236 TCDEP1 TROPICAL STORM VANCE DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212014 800 PM PDT FRI OCT 31 2014 Most of the available intensity analyses indicate that Vance has weakened since the previous advisory and is barely holding on to tropical cyclone status at that. The initial intensity of 35 kt is based on a blend of satellite intensity estimates of 35 kt, 30 kt, and 33 kt from TAFB, SAB, and UW-CIMSS ADT, respectively. Visible and microwave fix positions over the past few hours suggest that Vance has been moving slowly westward or just south of due west, so the initial motion estimate is now 270/05 kt. Otherwise, there is no significant change to the previous forecast track or reasoning. A general westward motion should continue through Saturday, followed by a turn to the west-northwest and northwest on Sunday as Vance moves around the southwestern periphery of a deep-layer ridge located to the north of the cyclone. As a mid-tropospheric trough approaches Baja California on Monday, Vance is forecast to move northward, followed by a turn and acceleration toward the northeast on Tuesday. The latest model guidance is in better agreement for this forecast cycle and is more tightly packed as well. Therefore, the new NHC forecast track is basically just an update of the previous advisory track, and closely follows the TVCE consensus track model. Although the convective cloud pattern of Vance has eroded significantly during the past several hours, a small burst of deep convection has recently developed over the center. Overall, however, the cyclone has maintained a well-developed low-level wind field. Dry mid-level air that has been plaguing Vance from the outset is expected to give way to a more moist environment in the 12-48 hour time period while the vertical wind shear remains rather low at less than 5 kt. The result is that Vance is forecast to gradually strengthen and become a hurricane by late Sunday. By 72 hours and beyond, southwesterly vertical shear is expected to sharply increase ahead of the aforementioned trough, causing the cyclone to rapidly weaken. However, it is worth noting that Vance could reach a higher peak intensity between the 48- and 72-hour periods before the weakening trend begins. The NHC intensity forecast is similar to the previous advisory forecast, and is a blend of the SHIPS and HWRF intensity models. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 9.5N 101.8W 35 KT 40 MPH 12H 01/1200Z 9.5N 103.0W 40 KT 45 MPH 24H 02/0000Z 10.0N 105.0W 45 KT 50 MPH 36H 02/1200Z 11.1N 107.1W 55 KT 65 MPH 48H 03/0000Z 12.6N 109.0W 65 KT 75 MPH 72H 04/0000Z 16.5N 110.3W 65 KT 75 MPH 96H 05/0000Z 20.1N 108.2W 40 KT 45 MPH 120H 06/0000Z 24.3N 105.3W 25 KT 30 MPH...INLAND $$ Forecaster Stewart

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Tropical Storm VANCE Forecast Discussion Number 7

2014-10-31 21:55:29| National Hurricane Center (East Pacific)

Issued at 200 PM PDT FRI OCT 31 2014 000 WTPZ41 KNHC 312055 TCDEP1 TROPICAL STORM VANCE DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212014 200 PM PDT FRI OCT 31 2014 Vance has a peculiar structure this afternoon. The central convection has become somewhat skeletal with the center exposed at times, although there are still plenty of curved banding features in the outer portion of the circulation. The culprit for this decrease in convection appears to be an influx of dry air moving into the central region of the tropical cyclone around the west and south sides. Dvorak estimates still support an intensity of about 40 kt. Since the dry air is close to the center now, it will probably take some time for this air to mix out. Thus little change is shown in the short term. Afterward, models insist that the large-scale environment will become favorable for strengthening over the next three days or so. Strong southwesterly shear is anticipated for the beginning of next week, which will probably cause Vance to weaken significantly at long range. There has not been much change to the guidance suite, with the majority of the guidance still showing Vance as a hurricane in a few days. The NHC forecast is therefore very close to the previous one, and generally lies between the intensity consensus and the SHIPS model. It seems that finally the motion of Vance has become more clear, now moving west-southwestward at about 6 kt. This general motion is expected through tonight due to a ridge over the eastern Pacific. This ridge should move eastward over the next few days, steering the cyclone more westward tomorrow, and to the northwest by late this weekend. Vance is then forecast to turn northward and then north- northeastward ahead of a trough moving over Baja California. Subtle differences in the speed of the trough are leading to increased model spread at long range, with the faster ECMWF preferring a more north-northeast track, compared to the slower GFS solution of a sharper northeastward turn. The NHC forecast is adjusted westward at day 3 and beyond, and is close to a dynamical model consensus excluding the UKMET model, which has an improbable forecast due to a seemingly spurious interaction with a weak ITCZ disturbance. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 9.5N 101.4W 40 KT 45 MPH 12H 01/0600Z 9.3N 102.4W 40 KT 45 MPH 24H 01/1800Z 9.6N 104.1W 45 KT 50 MPH 36H 02/0600Z 10.5N 106.2W 55 KT 65 MPH 48H 02/1800Z 11.7N 108.4W 65 KT 75 MPH 72H 03/1800Z 16.0N 110.5W 70 KT 80 MPH 96H 04/1800Z 19.8N 108.5W 50 KT 60 MPH 120H 05/1800Z 23.5N 106.0W 30 KT 35 MPH...INLAND $$ Forecaster Blake

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Tropical Storm VANCE Forecast Discussion Number 6

2014-10-31 15:38:16| National Hurricane Center (East Pacific)

Issued at 800 AM PDT FRI OCT 31 2014 000 WTPZ41 KNHC 311438 TCDEP1 TROPICAL STORM VANCE DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212014 800 AM PDT FRI OCT 31 2014 There hasn't been a lot of significant change with the structure of Vance during the past several hours. While the central convection has weakened some, the convection associated with a banding feature on the east side has increased. Dvorak estimates are similar to 6 hours ago, so the initial wind speed will remain 40 kt. Vance continues to struggle with southwesterly shear and dry air. Most of the models, however, suggest that the shear should abate over the weekend, with increasing moisture and upper-level divergence expected as well. The latest model guidance generally shows a higher peak intensity, and the NHC forecast is now a bit higher at 48-72 hours. After that time, a significant increase in southwesterly shear is forecast, which will likely cause weakening while the cyclone approaches Mexico. The center has not been easy to track with this cyclone, but the latest microwave and visible satellite data suggest it has been creeping toward the south-southwest. A ridge over the eastern Pacific is expected to move eastward over the next few days, steering the cyclone more steadily west-southwestward by late today, westward tomorrow, and to the northwest by late this weekend. Vance is then forecast to turn northward and then northeastward ahead of a trough moving over Baja California. While the models are in good agreement on the overall track, there remains some spread in the timing of the turn toward Mexico. The guidance is generally faster than the last cycle, so the updated NHC forecast follows that trend. Overall the forecast is also little east of the previous one, mostly because of the initial motion and position. FORECAST POSITIONS AND MAX WINDS INIT 31/1500Z 10.1N 100.8W 40 KT 45 MPH 12H 01/0000Z 9.7N 101.7W 45 KT 50 MPH 24H 01/1200Z 9.6N 103.2W 50 KT 60 MPH 36H 02/0000Z 10.2N 105.2W 55 KT 65 MPH 48H 02/1200Z 11.4N 107.0W 65 KT 75 MPH 72H 03/1200Z 15.0N 109.3W 75 KT 85 MPH 96H 04/1200Z 19.3N 107.9W 55 KT 65 MPH 120H 05/1200Z 23.5N 105.0W 30 KT 35 MPH...INLAND $$ Forecaster Blake

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Tropical Storm VANCE Forecast Discussion Number 4

2014-10-31 03:34:13| National Hurricane Center (East Pacific)

Issued at 800 PM PDT THU OCT 30 2014 000 WTPZ41 KNHC 310234 TCDEP1 TROPICAL STORM VANCE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212014 800 PM PDT THU OCT 30 2014 Vance has strengthened a little this evening. Infrared satellite images indicate that deep convection has increased slightly to the northeast of the center and in a band on the south and east sides of the circulation. A blend of the latest Dvorak intensity estimates from TAFB, SAB, and the University of Wisconsin-CIMSS supports raising the initial wind speed to 40 kt. Southerly to southwesterly shear and dry air in the low- to mid-levels of the atmosphere are currently affecting Vance, and these conditions are expected to persist for about another day. Therefore, only slow strengthening is predicted during that time. Over the weekend, however, the atmosphere is expected to moisten near the storm while the shear lessens, providing a better opportunity for more significant strengthening. By the end of the forecast period, the global models show a sharp increase in southwesterly shear, which should cause the cyclone to begin weakening. The NHC intensity forecast lies between the SHIPS model and the intensity model consensus. The storm has been moving slowly west-southwestward during the past 6 to 12 hours. A mid-level ridge located to the north and northwest of Vance is expected to steer the cyclone west-southwestward to westward during the next day or two. After that time, a gradual turn to the north and then northeast is forecast as the ridge weakens and shifts eastward in response to an approaching large trough. Although the models are in agreement in the large-scale steering pattern, there is a fair amount of spread in where Vance turns northward. The NHC track forecast has been adjusted a little to the left of the previous one for the first 72 hours to be in better agreement with the latest guidance. FORECAST POSITIONS AND MAX WINDS INIT 31/0300Z 10.8N 101.3W 40 KT 45 MPH 12H 31/1200Z 10.4N 102.0W 45 KT 50 MPH 24H 01/0000Z 10.0N 103.3W 50 KT 60 MPH 36H 01/1200Z 9.9N 105.1W 50 KT 60 MPH 48H 02/0000Z 10.4N 107.0W 55 KT 65 MPH 72H 03/0000Z 12.9N 110.2W 70 KT 80 MPH 96H 04/0000Z 17.1N 110.4W 65 KT 75 MPH 120H 05/0000Z 20.5N 107.5W 45 KT 50 MPH $$ Forecaster Cangialosi

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Tropical Storm VANCE Forecast Discussion Number 3

2014-10-30 21:34:12| National Hurricane Center (East Pacific)

Issued at 200 PM PDT THU OCT 30 2014 000 WTPZ41 KNHC 302034 TCDEP1 TROPICAL STORM VANCE DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212014 200 PM PDT THU OCT 30 2014 Visible satellite images show that the center of the cyclone remains near the southwestern edge of the deep convection. Still, the convective organization has improved from a few hours ago, with a distinct band on the northeast side of the system. Dvorak estimates and scatterometer data support an initial wind speed of 35 kt for this advisory. Vance is the 20th named storm of the eastern North Pacific hurricane season, the most number of named storms in the basin since 1992. The scatterometer data suggests that Vance is now moving about 260/4. A southwestward motion is expected tomorrow as a ridge builds to the north of the cyclone. The storm should turn westward and west-northwestward by 72 hours while it moves across the southwestern periphery of the ridge. Vance will likely turn northward or north-northeastward at long range ahead of a mid-latitude trough diving over Baja California into the eastern Pacific. While there is broad agreement on the general synoptic pattern, the models have a stronger ridge than the last cycle, leading to the storm moving farther to the west and south. This shift in the steering has led to a slower solution at long range by almost every reliable model. The official NHC prediction is shifted westward and southward throughout the forecast period, and further adjustments could be required on the next advisory if model trends continue. Although Vance is expected to remain over warm water for the next several days, it is currently struggling with dry air entrainment and southwesterly shear. Most of the models respond to this environment by showing little significant intensity change during the next 24 hours, so the official forecast will follow suit. After that time, the global models continue to show reduced shear, with an increase in low- to mid-level moisture. These conditions should allow for Vance to become a hurricane in a few days, although guidance is not in particularly good agreement on this scenario. At long range, there is high uncertainty in the intensity forecast, with the models generally showing more shear than the last cycle. Thus the intensity prediction is lowered some from the previous NHC forecast, although it remains on the higher side of the guidance. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 11.0N 101.0W 35 KT 40 MPH 12H 31/0600Z 10.6N 101.6W 40 KT 45 MPH 24H 31/1800Z 10.1N 102.5W 40 KT 45 MPH 36H 01/0600Z 9.9N 104.0W 45 KT 50 MPH 48H 01/1800Z 10.1N 105.9W 50 KT 60 MPH 72H 02/1800Z 12.0N 109.6W 65 KT 75 MPH 96H 03/1800Z 16.0N 110.5W 70 KT 80 MPH 120H 04/1800Z 20.0N 108.5W 60 KT 70 MPH $$ Forecaster Blake

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