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Tropical Storm RACHEL Forecast Discussion Number 6

2014-09-25 22:48:38| National Hurricane Center (East Pacific)

Issued at 200 PM PDT THU SEP 25 2014 000 WTPZ43 KNHC 252048 TCDEP3 TROPICAL STORM RACHEL DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182014 200 PM PDT THU SEP 25 2014 After strengthening earlier today, Rachel appears to have leveled off in intensity this afternoon. The initial wind speed is held at a possibly generous 45 kt based on the latest satellite intensity estimates from TAFB, SAB, and UW-CIMSS. The low-level center of the storm is located near the northeastern edge of the main area of deep convection due to about 15 kt of shear. This shear is expected to lessen during the next couple of days, which should allow Rachel to gain strength. By the end of the weekend and early next week, the cyclone is expected to move over cooler water, and into an atmosphere of southwesterly shear and drier air. These unfavorable conditions should cause a weakening trend. The NHC intensity forecast is a little lower than the previous one in the short term, but is otherwise unchanged and is near the SHIPS guidance. Rachel is moving west-northwestward at about 12 kt steered by mid-level ridging to its north and northeast. A large trough currently offshore of the west coast of the U.S. is expected to move eastward causing the ridge to weaken and shift eastward as well. This change in the synoptic pattern should cause Rachel to gradually turn northward during the next few days. By the end of the forecast period, the weakening system is expected to slow down or become stationary when it becomes embedded in weak low-level steering currents. The NHC track forecast is a little to the left of the previous one and slower at the end of the period, following the trend in the latest guidance. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 17.0N 110.8W 45 KT 50 MPH 12H 26/0600Z 17.7N 112.3W 45 KT 50 MPH 24H 26/1800Z 18.7N 113.9W 50 KT 60 MPH 36H 27/0600Z 19.5N 115.0W 55 KT 65 MPH 48H 27/1800Z 20.4N 115.8W 60 KT 70 MPH 72H 28/1800Z 22.0N 116.1W 55 KT 65 MPH 96H 29/1800Z 22.8N 115.9W 45 KT 50 MPH 120H 30/1800Z 23.1N 115.5W 30 KT 35 MPH $$ Forecaster Cangialosi

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Tropical Storm RACHEL Forecast Discussion Number 4

2014-09-25 10:32:04| National Hurricane Center (East Pacific)

Issued at 200 AM PDT THU SEP 25 2014 000 WTPZ43 KNHC 250831 TCDEP3 TROPICAL STORM RACHEL DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182014 200 AM PDT THU SEP 25 2014 Microwave data reveal that Rachel is still a sheared cyclone with the center located to the northeast of the deep convection due to strong upper-level northeasterly winds. The cloud pattern has changed little, and Dvorak T-numbers from TAFB, SAB and ADT from CIMMS support an initial intensity of 35 kt. There is an opportunity for Rachel to strengthen a little during the next 2 to 3 days as the shear decreases. After that time, the shear is forecast to increase again, and the circulation will begin to move over cooler waters, resulting in gradual weakening. Microwave and conventional satellite fixes indicate that Rachel is moving toward the west-northwest or 295 degrees at 11 kt. The ridge over Mexico which is controlling the track of Rachel is forecast to weaken as a strong mid-latitude trough approaches. This steering pattern should favor a turn to the northwest and north beyond 48 hours. In fact, track models are in better agreement and now most of them favor a northward turn and a recurvature with a decrease in forward speed by the end of the forecast period. By then, Rachel is expected to be a weakening depression or a remnant low. The NHC forecast is very similar to the previous one through 3 days. After that time, it was adjusted eastward a little bit to follow the multi-model consensus TVCE. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 16.0N 108.6W 35 KT 40 MPH 12H 25/1800Z 16.8N 110.1W 35 KT 40 MPH 24H 26/0600Z 17.8N 112.0W 40 KT 45 MPH 36H 26/1800Z 18.7N 113.6W 45 KT 50 MPH 48H 27/0600Z 19.5N 114.7W 45 KT 50 MPH 72H 28/0600Z 21.0N 115.5W 45 KT 50 MPH 96H 29/0600Z 22.0N 115.5W 40 KT 45 MPH 120H 30/0600Z 23.5N 115.0W 30 KT 35 MPH $$ Forecaster Avila

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Tropical Storm RACHEL Forecast Discussion Number 3

2014-09-25 04:42:01| National Hurricane Center (East Pacific)

Issued at 800 PM PDT WED SEP 24 2014 000 WTPZ43 KNHC 250241 TCDEP3 TROPICAL STORM RACHEL DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182014 800 PM PDT WED SEP 24 2014 Vigorous deep convection has expanded in association with the tropical cyclone this evening, primarily in the southwestern semicircle. The asymmetric distribution of thunderstorms around the system is due to about 25 kt of northeasterly vertical shear being caused by a strong upper-level anticyclone to its north. The current intensity is based upon 35 kt estimates from both the Satellite Analysis Branch and the Advanced Dvorak Technique, though the Tropical Analysis and Forecast Branch suggests a slightly stronger system. Thus the cyclone is now named Tropical Storm Rachel. The system may gradually intensify during the next two to three days as the shear diminishes some. However, Rachel should also encounter cooler sea surface temperatures and drier low-level air as it moves toward the west-northwest. The system is expected to peak in intensity as a moderate tropical storm around day 2 or 3, followed by a gradual weakening. The NHC official intensity forecast is based upon the tightly clustered IVCN multi-model ensemble and is about the same as the previous advisory. The earlier ASCAT scatterometer pass suggested a radius of maximum wind of around 40 nm, which helped to define the tropical-storm- force wind radii now that the cyclone has strengthened. The global and regional hurricane models suggest that Rachel will remain rather small in size. A blend of these models with the climatology- persistence technique is the basis for the NHC wind radii predictions. A 2333Z SSMIS microwave image assisted in locating the center of Rachel, as the low-level swirl has remain tucked just under the convective overcast. Rachel is moving toward the west at about 10 kt. The tropical storm should turn toward the west-northwest during the next two days as it moves around the periphery of the mid-level subtropical ridge. In about three days, a strong short wave trough will be passing north of Rachel over California. The new 18Z GFS and the hurricane models run from it respond by turning Rachel northeastward toward Baja California, while the older 12Z ECMWF and UK Met Office global models continue moving a weaker Rachel west-northwestward. The NHC official track splits the difference and is slightly eastward from that of the previous advisory, but not as far eastward as the TVCE multi-model ensemble. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 15.3N 107.4W 35 KT 40 MPH 12H 25/1200Z 15.8N 108.8W 35 KT 40 MPH 24H 26/0000Z 16.9N 110.7W 40 KT 45 MPH 36H 26/1200Z 17.9N 112.5W 40 KT 45 MPH 48H 27/0000Z 18.6N 113.9W 45 KT 50 MPH 72H 28/0000Z 19.7N 115.5W 45 KT 50 MPH 96H 29/0000Z 20.5N 116.0W 40 KT 45 MPH 120H 30/0000Z 21.5N 116.0W 30 KT 35 MPH $$ Forecaster Landsea

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Tropical Depression EIGHTEEN-E Forecast Discussion Number 2

2014-09-24 22:37:02| National Hurricane Center (East Pacific)

Issued at 200 PM PDT WED SEP 24 2014 000 WTPZ43 KNHC 242036 TCDEP3 TROPICAL DEPRESSION EIGHTEEN-E DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182014 200 PM PDT WED SEP 24 2014 Deep convection formed closer to the center of the depression late this morning, but recent satellite imagery suggests that strong upper-level winds are beginning to cause a separation between the center and the convection once again. Dvorak intensity estimates were unchanged at 1800 UTC and a recent ASCAT pass indicated maximum winds of around 30 kt. Strong upper-level northeasterly winds are expected to prevent significant strengthening during the next 12 to 24 hours, however the depression could become a low-end tropical storm during this time. The shear is forecast to decrease late Thursday and Friday, which should allow for some modest strengthening before the cyclone moves into less favorable thermodynamic conditions late in the period. The updated NHC intensity forecast is similar to the previous advisory and is again close to the SHIPS guidance. The initial motion estimate is 280/12, a little more westward than estimated earlier today. The model guidance indicates that the cyclone should turn west-northwestward and continue on that general heading during the next several days, to the south of a mid-level ridge over northern Mexico. Later in the period, the cyclone should turn northwestward as a weakness in the ridge develops along 115W. The GFS continues to show a slightly stronger cyclone turning northward, while the ECMWF takes a weaker system westward. The NHC track lies between these solutions and is close to the multi-model consensus. The updated track is a little west of the previous advisory, primarily due to the more southward and westward initial position. FORECAST POSITIONS AND MAX WINDS INIT 24/2100Z 15.1N 106.8W 30 KT 35 MPH 12H 25/0600Z 15.7N 108.4W 30 KT 35 MPH 24H 25/1800Z 16.7N 110.5W 35 KT 40 MPH 36H 26/0600Z 17.7N 112.3W 35 KT 40 MPH 48H 26/1800Z 18.5N 114.1W 40 KT 45 MPH 72H 27/1800Z 19.7N 116.0W 45 KT 50 MPH 96H 28/1800Z 20.5N 116.8W 45 KT 50 MPH 120H 29/1800Z 21.5N 117.0W 40 KT 45 MPH $$ Forecaster Brown

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Tropical Depression POLO Forecast Discussion Number 25

2014-09-22 10:32:18| Tropical Depression LIDIA

Issued at 200 AM PDT MON SEP 22 2014

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