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Tropical Storm NORA Forecast Discussion Number 5

2015-10-10 16:39:56| National Hurricane Center (East Pacific)

Issued at 800 AM PDT SAT OCT 10 2015 000 WTPZ43 KNHC 101439 TCDEP3 TROPICAL STORM NORA DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182015 800 AM PDT SAT OCT 10 2015 The satellite appearance of Nora has improved slightly during the past several hours with deeper convection near the center and increased banding features in the northwestward quadrant. The initial intensity is raised to 40 kt as a compromise between the TAFB and SAB satellite estimates. Further strengthening seems likely over the next couple of days while Nora remains in a low shear, warm water environment. The models, however, generally show a lower peak intensity with Nora, perhaps due to drier air in the mid-levels, so the new forecast will reflect this trend. The most notable change to the forecast is at day 3 and beyond when the global models are predicting the vertical wind shear to increase earlier and be much stronger than predicted yesterday for the cyclone. Intensity guidance is notably lower during that period, with only the GFDL showing hurricane strength. The latest NHC prediction is similar to the previous one through 48 hours, then is reduced afterward by about 10 kt. That's about the largest change I feel comfortable making at long range due to continuity concerns, but most of the historically reliable guidance is still below my new forecast. Nora is moving westward at roughly 12 kt. The cyclone should move to the west or west-northwest for the next couple of days while it is steered by a ridge over the east-central Pacific. This ridge is forecast to weaken during that time, which should result in Nora slowing down and gradually gaining latitude. A mid-latitude trough should help the ridge break down in a few days and turn Nora northward, although there remains some spread in the guidance when Nora will recurve. The GFS and HWRF models have joined the ECMWF model in predicting a weaker Nora, which results in a delayed northward turn. The official forecast is similar to the previous one through 72 hours, then is shifted westward at long range in accordance with the new guidance. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 11.7N 137.2W 40 KT 45 MPH 12H 11/0000Z 11.9N 139.0W 45 KT 50 MPH 24H 11/1200Z 12.1N 140.9W 50 KT 60 MPH 36H 12/0000Z 12.3N 142.5W 60 KT 70 MPH 48H 12/1200Z 12.6N 143.7W 65 KT 75 MPH 72H 13/1200Z 13.6N 145.3W 65 KT 75 MPH 96H 14/1200Z 15.9N 145.4W 55 KT 65 MPH 120H 15/1200Z 18.0N 144.5W 45 KT 50 MPH $$ Forecaster Blake

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Tropical Storm NORA Forecast Discussion Number 4

2015-10-10 10:43:57| National Hurricane Center (East Pacific)

Issued at 200 AM PDT SAT OCT 10 2015 000 WTPZ43 KNHC 100843 TCDEP3 TROPICAL STORM NORA DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182015 200 AM PDT SAT OCT 10 2015 Nora has changed little in organization during the past several hours. The low-level center continues to be near the southeastern edge of the convection, and the strongest convection is currently in outer bands well northwest of the center. This is likely due to the effects of light southeasterly vertical wind shear. In addition, recent ASCAT data suggests the circulation is elongated north to south. Satellite intensity estimates are 35 kt from both TAFB and SAB, and the ASCAT data also shows winds near 35 kt. Based on this, the advisory intensity remains 35 kt. Nora is now moving 285/14, with the cyclone continuing to be steered by a deep-layer subtropical ridge to the north. The dynamical models forecast the ridge to weaken during the next 36 hours, with Nora moving generally westward with a decrease in forward speed. After that time, the tropical cyclone is likely to turn northward and probably recurve as a deep-layer trough over the north Pacific breaks the subtropical ridge. The track guidance is tightly clustered for the first 36 hours, but subsequently there is an increased spread on where and how fast Nora will recurve. The ECMWF shows a weaker Nora moving farther west and eventually turning northward along 149W by 120 hours. The UKMET shows a stronger Nora making an earlier recurvature with the storm near 19N 138W by 120 hours. The GFS lies between these models and is near the center of the guidance envelope. The new track forecast is a little north of the previous forecast for the first 48 hours, and then it is a little west of the previous forecast after that time. The new track is near the center of the guidance envelope and lies a little west of the GFS after 72 hours. Nora is expected to remain in an environment of light shear and warm sea surface temperatures for the next 2-3 days, which should allow strengthening. After that, the cyclone is expected to encounter unfavorable conditions of strong southwesterly shear and decreasing sea surface temperatures. Based on this, the new intensity forecast follows the trend of the previous forecast in calling to Nora to peak as a hurricane in about 72 hours and subsequently weaken to a tropical storm by 120 hours. The new forecast is in best agreement with the Florida State Superensemble. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 11.6N 136.5W 35 KT 40 MPH 12H 10/1800Z 11.9N 138.3W 45 KT 50 MPH 24H 11/0600Z 12.1N 140.5W 50 KT 60 MPH 36H 11/1800Z 12.4N 142.3W 60 KT 70 MPH 48H 12/0600Z 12.7N 143.7W 65 KT 75 MPH 72H 13/0600Z 13.5N 145.5W 75 KT 85 MPH 96H 14/0600Z 16.0N 145.0W 70 KT 80 MPH 120H 15/0600Z 18.5N 142.5W 60 KT 70 MPH $$ Forecaster Beven

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Tropical Storm NORA Forecast Discussion Number 3

2015-10-10 04:34:24| National Hurricane Center (East Pacific)

Issued at 800 PM PDT FRI OCT 09 2015 000 WTPZ43 KNHC 100234 TCDEP3 TROPICAL STORM NORA DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182015 800 PM PDT FRI OCT 09 2015 Deep convection has increased a little since the last advisory, with the center located on the southeastern edge of the convective mass due to light/moderate southeasterly shear over the cyclone. The initial intensity is set to 35 kt based on the latest Dvorak classifications from TAFB and SAB, marking the formation of Tropical Storm Nora, the 14th tropical storm of the eastern North Pacific season. Environmental conditions appear favorable for continued steady strengthening for the next 72 hours, with the cyclone moving over SSTs at or above 29C during that period and light shear. By days 4 and 5 the SHIPS model and global model fields show the shear increasing, which should result in weakening. The new NHC forecast is largely an update of the previous one, and is close to or a little above the SHIPS model through the period. The initial motion estimate is 275/14, as Nora is being steered quickly westward by a subtropical ridge to the north. A gradual decrease in forward speed is forecast during the next 36 hours as the ridge slowly weakens, and Nora should then turn west- northwestward as a weakness develops around 145W. Nora is then forecast to recurve between a deep-layer trough over the north- central Pacific and a strengthening ridge to the southeast by the end of the period. The track model guidance is in overall good agreement on this scenario, and the new NHC forecast is close to a blend of the GFS and ECMWF models through the period. The new official forecast is a little north of the previous one through 48 hours, and then is a little to the left, showing a more gradual recurvature following the latest trend in the guidance. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 11.3N 135.1W 35 KT 40 MPH 12H 10/1200Z 11.6N 137.0W 40 KT 45 MPH 24H 11/0000Z 11.8N 139.5W 50 KT 60 MPH 36H 11/1200Z 11.9N 141.6W 60 KT 70 MPH 48H 12/0000Z 12.3N 143.1W 65 KT 75 MPH 72H 13/0000Z 13.0N 145.0W 80 KT 90 MPH 96H 14/0000Z 15.0N 145.0W 75 KT 85 MPH 120H 15/0000Z 18.5N 142.5W 65 KT 75 MPH $$ Forecaster Brennan

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Tropical Depression EIGHTEEN-E Forecast Discussion Number 2

2015-10-09 22:38:02| National Hurricane Center (East Pacific)

Issued at 200 PM PDT FRI OCT 09 2015 000 WTPZ43 KNHC 092037 TCDEP3 TROPICAL DEPRESSION EIGHTEEN-E DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182015 200 PM PDT FRI OCT 09 2015 The depression has not changed much since the previous advisory. The associated deep convection is organized in a curved band to the north and west of the center with a more linear swath of clouds a couple of hundred n mi to the northeast of the center. The Dvorak classifications from TAFB, SAB, and UW-CIMSS ADT remain 2.0/30 kt, and a recent ASCAT pass also showed winds around that value. Based on these data, the initial wind speed remains 30 kt. The depression is moving westward at about 14 kt steered by a subtropical ridge to its north. This general heading with a decrease in forward speed is expected during the next 2-3 days while the ridge weakens. After that time, a turn toward the north and then northeast is predicted when the system becomes embedded in the flow ahead of a large trough. The official track forecast is a little to the south of the previous one in the short term, mainly due to the more southward initial motion, and then slightly to the east of the previous track to come into better agreement with the latest models. Environmental conditions are expected to be conducive for strengthening during the next few days, and accordingly most of the guidance shows the cyclone intensifying. The SHIPS model shows the shear increasing in 4 to 5 days, and that, along with more stable air and decreasing SSTs, should end the strengthening trend and induce weakening. The official intensity forecast is unchanged from the previous one, and remains near the high end of the guidance. FORECAST POSITIONS AND MAX WINDS INIT 09/2100Z 10.9N 133.5W 30 KT 35 MPH 12H 10/0600Z 11.1N 135.3W 35 KT 40 MPH 24H 10/1800Z 11.4N 137.8W 45 KT 50 MPH 36H 11/0600Z 11.6N 140.1W 55 KT 65 MPH 48H 11/1800Z 11.8N 141.9W 65 KT 75 MPH 72H 12/1800Z 12.5N 144.2W 85 KT 100 MPH 96H 13/1800Z 14.3N 144.8W 80 KT 90 MPH 120H 14/1800Z 17.3N 143.2W 70 KT 80 MPH $$ Forecaster Cangialosi

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Tropical Depression EIGHTEEN-E Forecast Discussion Number 1

2015-10-09 16:53:20| National Hurricane Center (East Pacific)

Issued at 800 AM PDT FRI OCT 09 2015 000 WTPZ43 KNHC 091453 TCDEP3 TROPICAL DEPRESSION EIGHTEEN-E DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182015 800 AM PDT FRI OCT 09 2015 Satellite images indicate that the area of low pressure in the far southwestern portion of the eastern Pacific has become better organized. Curved banding features have increased, along with a growing area of deep convection near the center. Thus the system is declared a tropical depression, the 18th of the season. The initial wind speed is set to 30 kt using the Dvorak estimate from TAFB. The minimum pressure is 1008 mb on the basis of buoy 43535 near the depression, which reported 1009 mb a couple of hours ago. The cyclone is expected to be in a favorable environment for strengthening for the next few days, with low wind shear, very warm waters and high mid-level moisture. Thus steady intensification is forecast until early next week. Thereafter, an increase in southwesterly shear and some cooler waters should cause the cyclone to weaken some by day 5. The official intensity prediction is on the high side of the intensity guidance, a reflection of both the conducive environment and the low bias of the guidance during this season. It would not be surprising if the cyclone intensified more than shown here given the large-scale environment, but timing this is not possible at this time. The depression is moving westward at about 12 kt. This general motion is expected for the next 2-3 days while it remains under the influence of the subtropical ridge located over the eastern and central Pacific. This pattern is expected to change quickly after day 3 when a mid-latitude trough erodes the ridge, causing the cyclone to recurve well east of the Hawaiian Islands. For a first forecast, the guidance is in rather good agreement, and the official forecast is close to the overall consensus, with a bit more weight on the ECMWF model. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 11.1N 132.0W 30 KT 35 MPH 12H 10/0000Z 11.3N 133.8W 35 KT 40 MPH 24H 10/1200Z 11.7N 136.2W 45 KT 50 MPH 36H 11/0000Z 12.0N 138.8W 55 KT 65 MPH 48H 11/1200Z 12.2N 140.9W 65 KT 75 MPH 72H 12/1200Z 12.8N 143.5W 85 KT 100 MPH 96H 13/1200Z 14.5N 145.0W 85 KT 100 MPH 120H 14/1200Z 17.0N 144.0W 75 KT 85 MPH $$ Forecaster Blake

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