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Tropical Storm RICK Forecast Discussion Number 7

2015-11-20 03:40:21| National Hurricane Center (East Pacific)

Issued at 800 PM MST THU NOV 19 2015 000 WTPZ41 KNHC 200240 TCDEP1 TROPICAL STORM RICK DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212015 800 PM MST THU NOV 19 2015 Rick's cloud pattern has eroded some during the past 6 hours with previously solid bands of convection in the northern semicircle having become more fragmented during the past few hours. In addition, numerous small arc cloud lines have been noted propagating away from the cyclone, which is indicative of dry mid-level air having penetrated into the inner core region. This supposition is further supported by a 20/0006 UTC AMSU pass indicating only a narrow fragmented band of convection is present in the northwestern quadrant of the storm. Therefore, the initial intensity of 35 kt remains unchanged for this advisory, which is lower than the available satellite intensity estimates. The initial motion estimate is 295/09 kt and is based primarily on passive microwave satellite data. A mid-level ridge over central Mexico is forecast to build westward to the north and east of Rick during the next 24-36 hours, while a large upper-level low located near 27N 138W is expected to fill and gradually open up into a broad trough by 48-72 hours. The combination of these two steering mechanisms should keep Rick moving west-northwestward for the next 48 hours, followed by a decrease in forward speed and a gradual turn toward the northwest and north at 72 h and 96 h, respectively. The official forecast track was only nudged slightly to the left of the previous advisory track, and essentially lies down the middle of NHC track guidance envelope. Rick is forecast to move into a weak vertical wind shear regime during the next 24-36 hours while remaining over SSTs of 29 deg C. These favorable conditions would normally support intensification of a tropical cyclone. However, the ragged and elongated inner-core wind field, coupled with additional entrainment of drier mid-level air, is expected to inhibit any significant development and organization of deep convection. By 48 hours and beyond, an increase in southwesterly vertical wind shear to more than 25 kt is forecast to induce gradual weakening, with Rick becoming a remnant low by 96 hours when the cyclone will be moving over cooler waters at that time. Rick is expected to dissipate day 5, if not sooner. NHC intensity forecast is a little lower than the previous advisory and remains below the multi-model consensus, IVCN. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 15.2N 108.1W 35 KT 40 MPH 12H 20/1200Z 15.9N 109.5W 40 KT 45 MPH 24H 21/0000Z 16.5N 111.1W 40 KT 45 MPH 36H 21/1200Z 17.2N 112.4W 40 KT 45 MPH 48H 22/0000Z 17.8N 113.4W 35 KT 40 MPH 72H 23/0000Z 19.5N 115.0W 25 KT 30 MPH 96H 24/0000Z 21.6N 115.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 25/0000Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm RICK Forecast Discussion Number 6

2015-11-19 21:41:57| National Hurricane Center (East Pacific)

Issued at 200 PM MST THU NOV 19 2015 000 WTPZ41 KNHC 192041 TCDEP1 TROPICAL STORM RICK DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212015 200 PM MST THU NOV 19 2015 Rick is exhibiting a shear pattern, with the low-level center of the cyclone estimated to be near the southeastern edge of a curved convective band over the northwestern semicircle of the circulation. A 1616 UTC ASCAT-A overpass indicated peak uncontaminated winds of 36 kt, so the initial intensity is held at 35 kt. Some further reduction in southeasterly shear over the cyclone should occur tonight or early Friday while other large- scale factors remain generally favorable, which could allow for some additional intensification over the next 24 hours or so. However, the broad nature of the cyclone's circulation shown by the scatterometer data is most likely to result in only slow strengthening before a substantial increase in west-southwesterly shear occurs in about 36 to 48 hours. Even higher shear is expected over Rick by 72 hours once the storm gains more latitude and a trough in the eastern Pacific subtropics nears the cyclone from the west. A rapid decoupling of the cyclone should occur not long after that time, and remnant low status is indicated in 96 hours, though this could occur sooner. The new intensity forecast is is a bit lower than the previous one and slightly lower than the multi-model consensus through 48 hours. ASCAT passes were quite helpful in determining that the location of Rick's low-level center was farther south and west than previously estimated. Those fixes indicate that Rick has turned northwestward with an initial motion estimate of 320/07. A mid-level ridge over mainland Mexico should build north of Rick tonight and tomorrow, resulting in a west-northwestward turn with an increase in forward speed. Once Rick reaches the western periphery of this ridge in about 3 days, a more poleward track is forecast until dissipation. The new track forecast is adjusted back to the left, primarily due the center re-location. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 14.8N 107.0W 35 KT 40 MPH 12H 20/0600Z 15.5N 108.3W 40 KT 45 MPH 24H 20/1800Z 16.2N 109.9W 45 KT 50 MPH 36H 21/0600Z 16.9N 111.6W 45 KT 50 MPH 48H 21/1800Z 17.5N 112.8W 40 KT 45 MPH 72H 22/1800Z 19.0N 114.4W 30 KT 35 MPH 96H 23/1800Z 21.2N 115.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 24/1800Z...DISSIPATED $$ Forecaster Kimberlain

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Tropical Storm RICK Forecast Discussion Number 5

2015-11-19 15:57:46| National Hurricane Center (East Pacific)

Issued at 900 AM CST THU NOV 19 2015 000 WTPZ41 KNHC 191457 TCDEP1 TROPICAL STORM RICK DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212015 900 AM CST THU NOV 19 2015 The cloud pattern of the cyclone is better organized than this time yesterday. First-light visible imagery indicates that the low-level center is underneath a circular mass of deep convection, and there has been an increase in banding features and their associated curvature. The increase in organization could be a sign of some decrease of the southeasterly shear that has been affecting the cyclone. A Dvorak intensity estimate of T2.5 from TAFB and an UW-CIMSS ADT value of 2.9 is used to raise the initial intensity estimate to 35 kt. Some further decrease in southeasterly shear is likely through early Friday. With large-scale environmental conditions otherwise largely favorable, intensification is shown through about 24 to 36 hours. The window of opportunity for strengthening should be short- lived though, since west-southwesterly shear is forecast to increase by 48 hours when Rick moves north of the upper-level ridge axis. The shear should become prohibitively high by 72 hours ahead of a shortwave trough in the eastern Pacific subtropics being ejected eastward toward the cyclone. The result should be rapid weakening, and remnant low status is likely by 96 hours, if not sooner. Dissipation is now shown by 120 hours. The new NHC intensity forecast is slightly above the previous one, and shows and earlier peak, with remnant low status indicated sooner. The center has been difficult to locate but seems to be slightly farther east than previous estimates based on a couple of microwave passes and visible imagery. The best estimate of the initial motion is north or 360/06. Global models show mid-level ridging building to the north of the cyclone today, and the depression should be respond by moving more quickly toward the northwest and then west-northwest over the next day or two. Rick should reach the western periphery of this ridge in 3 to 4 days and begin to move more poleward, but will likely dissipate before responding to the trough in the subtropics moving toward it. The new track forecast is right of the previous one, primarily due to the more eastward initial position estimate. Only 3 tropical storms have formed later than this calendar date in the eastern North Pacific since reliable records began in the early 1970s. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 14.7N 105.8W 35 KT 40 MPH 12H 20/0000Z 15.2N 106.5W 40 KT 45 MPH 24H 20/1200Z 16.2N 108.5W 50 KT 60 MPH 36H 21/0000Z 17.1N 110.6W 50 KT 60 MPH 48H 21/1200Z 17.7N 112.0W 45 KT 50 MPH 72H 22/1200Z 19.0N 113.4W 35 KT 40 MPH 96H 23/1200Z 20.9N 114.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 24/1200Z...DISSIPATED $$ Forecaster Kimberlain

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Tropical Depression TWENTY-ONE-E Forecast Discussion Number 4

2015-11-19 09:35:46| National Hurricane Center (East Pacific)

Issued at 200 AM MST THU NOV 19 2015 000 WTPZ41 KNHC 190835 TCDEP1 TROPICAL DEPRESSION TWENTY-ONE-E DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212015 200 AM MST THU NOV 19 2015 Tropical Depression Twenty-One-E remains poorly organized. While the convection has increased during the past several hours, the low-level center appears to be east of the southern end of the convective area due to ongoing southeasterly shear. Satellite intensity estimates are 30 kt from both TAFB and SAB, and thus the initial intensity is unchanged from the previous advisory. The initial motion is a rather uncertain 355/5. A developing mid- to upper-level ridge to the north and northeast of the depression should result in a turn toward the west-northwest during the next 24 hours, with this motion continuing through 48 hours. After that time, a mid-latitude westerly trough moving into the northeastern Pacific should break the ridge with the depression turning northwestward and northward. While the guidance is in general agreement with this scenario, after 72 hours there is still a significant spread as to where the depression may make the northward turn. The new forecast track is a little to the south of the multi-model consensus through 72 hours, then is a little east of it after that time. The depression is expected to remain over warm sea surface temperatures for the next three days or so, and the current shear is forecast to subside to low values between 12-48 hours. However, despite these apparently favorable conditions, the intensity guidance forecasts only modest strengthening during the next couple of days. After that time, increasing southwesterly shear and decreasing sea surface temperatures should cause the cyclone to weaken. The new intensity forecast is the same as the previous forecast, and it lies near the upper edge of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 13.7N 106.1W 30 KT 35 MPH 12H 19/1800Z 14.4N 106.7W 35 KT 40 MPH 24H 20/0600Z 15.2N 108.3W 40 KT 45 MPH 36H 20/1800Z 16.0N 110.0W 45 KT 50 MPH 48H 21/0600Z 16.7N 111.4W 45 KT 50 MPH 72H 22/0600Z 18.0N 113.5W 40 KT 45 MPH 96H 23/0600Z 19.5N 114.5W 30 KT 35 MPH 120H 24/0600Z 21.5N 114.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Tropical Depression TWENTY-ONE-E Forecast Discussion Number 3

2015-11-19 03:35:18| National Hurricane Center (East Pacific)

Issued at 800 PM MST WED NOV 18 2015 000 WTPZ41 KNHC 190235 TCDEP1 TROPICAL DEPRESSION TWENTY-ONE-E DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212015 800 PM MST WED NOV 18 2015 The depression is poorly organized with the low-level center well separated from the mid-level circulation as indicated by several microwave images. Similar to earlier today, the low-level center continues to be located to the southeast of the weakening convection, indicating that southeasterly shear still prevails. Initial intensity remains at 30 kt based on satellite estimates from TAFB and SAB. There is an opportunity for the depression to strengthen slightly during the next day or two, while a narrow ridge builds to the north of the cyclone and the shear decreases. Most of the intensity models forecast some increase in the winds, and so does the NHC forecast. In fact, the NHC forecast still brings the depression to tropical storm status in about 12 to 24 hours. However, by the end of the forecast period, the effects of cooler waters and dry air should result in weakening. The center has moved very little during the past several hours, or perhaps it has has been drifting eastward and then northward around a larger cyclonic gyre. Most of the global models build a ridge to the north of the cyclone soon, and this steering pattern should force the depression to begin to move on a west-northwest track early Thursday. It should then continue with this general motion for the next 2 to 3 days. After that time, a new mid-latitude trough is forecast to approach from the west, weakening the ridge and inducing a northward motion. However, there is little confidence in the track forecast by the end of the period due to large spread in the model tracks. The NHC forecast follows closely the multi-model consensus, and is a little to the east of the previous NHC forecast beyond 3 days. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 13.2N 106.1W 30 KT 35 MPH 12H 19/1200Z 13.7N 106.5W 35 KT 40 MPH 24H 20/0000Z 14.6N 108.2W 40 KT 45 MPH 36H 20/1200Z 15.5N 110.0W 45 KT 50 MPH 48H 21/0000Z 16.0N 111.0W 45 KT 50 MPH 72H 22/0000Z 17.5N 113.0W 40 KT 45 MPH 96H 23/0000Z 19.0N 114.0W 30 KT 35 MPH 120H 24/0000Z 21.0N 114.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Avila

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