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Tropical Storm ROSLYN Forecast Discussion Number 5

2016-09-26 16:42:51| National Hurricane Center (East Pacific)

Issued at 800 AM PDT MON SEP 26 2016 000 WTPZ43 KNHC 261442 TCDEP3 TROPICAL STORM ROSLYN DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182016 800 AM PDT MON SEP 26 2016 Roslyn remains a large, but sheared tropical storm. An 0847 UTC AMSR microwave overpass indicates that the low-level center is located well to west of the large area of deep convection, due to moderate southwesterly shear. Dvorak intensity estimates from TAFB and SAB are unchanged from before, so the initial intensity is kept at 35 kt for this advisory. The southwesterly shear that is currently affecting the cyclone is predicted to increase during the next 24 hours, which should prevent significant strengthening while Roslyn remains over marginally warm water. In a little more than 24 hours, the tropical storm will be crossing the 26 deg C isotherm and moving into a more stable air mass, which should begin the weakening process. The NHC forecast shows Roslyn becoming a remnant low within 48 hours, and dissipating by the end of the forecast period. Recent fixes suggest that Roslyn is moving north-northeastward or 015/4 kt. The tropical storm should turn northeastward today in the southwesterly flow between a mid-level ridge to the southeast and a large mid- to upper-level low over the Baja California peninsula. After Roslyn weakens into a shallow remnant low, it should turn northward and then northwestward in the low-level flow west of the Baja peninsula. The new NHC track forecast is very similar to the previous advisory, and is a blend of the GFS, ECMWF, and GFS ensemble mean. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 17.0N 119.4W 35 KT 40 MPH 12H 27/0000Z 17.5N 119.0W 35 KT 40 MPH 24H 27/1200Z 18.5N 118.1W 35 KT 40 MPH 36H 28/0000Z 19.7N 117.3W 30 KT 35 MPH 48H 28/1200Z 21.0N 117.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 29/1200Z 23.2N 118.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 30/1200Z 24.5N 119.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 01/1200Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm ROSLYN Forecast Discussion Number 4

2016-09-26 10:35:49| National Hurricane Center (East Pacific)

Issued at 200 AM PDT MON SEP 26 2016 000 WTPZ43 KNHC 260835 TCDEP3 TROPICAL STORM ROSLYN DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182016 200 AM PDT MON SEP 26 2016 The sheared cloud pattern in infrared satellite imagery has changed little since the previous advisory. However, a 0304Z SSMI/S pass indicated the low-level structure had improved markedly, with a sharp hooked band wrapping more than half around the now well-defined low-level circulation center. The initial intensity has been increased to 35 kt based on a Dvorak classification of T2.5/35 kt from TAFB and the improved low-level structure indicated in SSMI/S 37 GHZ data. This makes Roslyn the seventeenth named storm of the 2016 eastern North Pacific hurricane season. The initial motion estimate is 020/4 kt. The advisory position had to be adjusted more than 30 nmi to the east of the previous advisory track based on recent SSMI/S and AMSU microwave center fixes. Otherwise, the previous track forecast rationale remains unchanged. A large mid- to upper-level low currently located over the central Baja California peninsula is expected to continue moving westward to west-southwestward during the next day or two. The combined southwesterly flow between that low and a deep-layer ridge located to the east and southeast of Roslyn should keep the tropical cyclone moving slowly north-northeastward to northeastward for the next 48 hours. After that, Roslyn is expected to weaken into a shallow remnant low, turning northward on day 3 and then northwestward on day 4. The new NHC track forecast is to the right of the previous advisory track, mainly due to the more eastward initial position, and lies close to the various consensus models. Little if any strengthening is expected due to gradually increasing southwesterly vertical wind shear and a very dry mid-level moisture regime characterized by humidity values less than 40 percent. By 36 to 48 hours, the vertical shear is forecast to increase to more than 30 kt, which is expected to erode the deep convection and induce steady weakening. As a result, Roslyn is forecast to become a remnant low by 48 hours, but this could occur sooner. The GFS and ECMWF models show the remnant low dissipating by the end of the forecast period when Roslyn will be moving over sub-24C SSTs. The new intensity forecast is identical to the previous advisory and closely follows the IVCN intensity consensus model. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 16.8N 119.5W 35 KT 40 MPH 12H 26/1800Z 17.2N 119.2W 35 KT 40 MPH 24H 27/0600Z 18.0N 118.5W 35 KT 40 MPH 36H 27/1800Z 19.1N 117.6W 35 KT 40 MPH 48H 28/0600Z 20.4N 117.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 29/0600Z 22.5N 117.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 30/0600Z 24.6N 119.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 01/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Depression EIGHTEEN-E Forecast Discussion Number 3

2016-09-26 04:43:47| National Hurricane Center (East Pacific)

Issued at 800 PM PDT SUN SEP 25 2016 000 WTPZ43 KNHC 260243 TCDEP3 TROPICAL DEPRESSION EIGHTEEN-E DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182016 800 PM PDT SUN SEP 25 2016 The cloud pattern of the depression has not changed much during the last several hours. The center of the system is partially exposed on the west side of a convective band. Satellite images also show a pronounced dry slot to the west and northwest of the center. The Dvorak classifications remain T2.5/35 kt from TAFB and T1.5/25 kt from SAB, and based on these estimates, the initial wind speed is held at 30 kt. Some slight strengthening is possible overnight or on Monday while the system remains over warm water and in an environment of light to moderate shear. After that time, the environment should become less conducive with southwesterly shear increasing to more than 20 kt in about 24 hours, which will likely end the opportunity for strengthening. The system is forecast to cross the 26-deg-C isotherm in 36 to 48 hours, and as a result, it should become a remnant low by day 3. The global models show the remnant low dissipating by the end of the forecast period, and that is reflected in the official forecast. The new intensity forecast is a little lower than the previous one and is in good agreement with the latest intensity model consensus. The center of the depression has wobbled a bit to the west of the previous track, and the current motion estimate is 345/6 kt. A large cut-off mid- to upper-level low over northwestern Mexico is expected to drift southwestward during the next day or two. This should cause the system to turn north-northeastward to northeastward on Monday, and continue in that general direction through mid-week. Once the system becomes a shallow remnant low, a turn to the west-northwest is predicted, following the low-level trade wind flow. The NHC track forecast is not too different from the previous one, and is in best agreement with the GFS ensemble mean and a consensus of the GFS and ECMWF models. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 16.7N 120.1W 30 KT 35 MPH 12H 26/1200Z 17.2N 119.8W 35 KT 40 MPH 24H 27/0000Z 17.8N 119.4W 35 KT 40 MPH 36H 27/1200Z 18.7N 118.7W 35 KT 40 MPH 48H 28/0000Z 19.9N 118.0W 30 KT 35 MPH 72H 29/0000Z 22.6N 117.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 30/0000Z 24.6N 119.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 01/0000Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Depression EIGHTEEN-E Forecast Discussion Number 1

2016-09-25 18:52:14| National Hurricane Center (East Pacific)

Issued at 1000 AM PDT SUN SEP 25 2016 000 WTPZ43 KNHC 251652 TCDEP3 TROPICAL DEPRESSION EIGHTEEN-E SPECIAL DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182016 1000 AM PDT SUN SEP 25 2016 Deep convection associated with the low pressure area located well southwest of the Baja California has become better organized overnight, and early morning visible satellite imagery indicate that the circulation has become better defined. Based on these observations, and Dvorak classifications of T2.0 and T1.5 from TAFB and SAB respectively, advisories are being initiated on a 30-kt tropical depression at this time. The depression is currently located over warm water and within an area of low vertical wind shear, which is favorable for some gradual strengthening today. However, in about 24 hours, the tropical cyclone is forecast to move into an area of higher southwesterly shear caused by large mid- to upper-level low and associated trough over northwestern Mexico. The global models suggest that the shear will become quite strong in 36 to 48 hours as the cyclone begins moving over cooler waters. This should result in a rapid spin down, and the system is likely to become a post-tropical remnant low within 3 days. The official intensity foreast is slightly above the SHIPS guidance but is in good agreement with the intensity consensus. Since the depression is still in its formative stage, the initial motion is a somewhat uncertain 360/4 kt. The cyclone is expected to be steered slowly northward or north-northeastward during the next couple of days around the western portion of a weak mid-level ridge that extends southwestward from southern Mexico. By 72 hours, the low should turn northwestward in the low-level steering flow after it weakens and becomes a vertically shallow system. Although the ECMWF and GFS models are on opposite sides of the guidance envelope, the track models are in general agreement on the overall scenario and the NHC forecast lies near the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 25/1700Z 15.6N 119.7W 30 KT 35 MPH 12H 26/0000Z 16.2N 119.6W 35 KT 40 MPH 24H 26/1200Z 16.8N 119.4W 40 KT 45 MPH 36H 27/0000Z 17.4N 119.1W 40 KT 45 MPH 48H 27/1200Z 18.5N 118.3W 40 KT 45 MPH 72H 28/1200Z 21.0N 117.3W 30 KT 35 MPH 96H 29/1200Z 23.0N 118.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 30/1200Z 24.5N 119.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Tropical Storm KARL Forecast Discussion Number 44

2016-09-25 10:41:12| National Hurricane Center (Atlantic)

Issued at 500 AM AST SUN SEP 25 2016 000 WTNT42 KNHC 250840 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 44 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 500 AM AST SUN SEP 25 2016 Karl continues to produce a large mass of cold-topped convection sheared to the northeast of the low-level center. Some of the cloud tops are as cold as -83 deg C, which is unusual for that far north. Earlier NASA/NOAA Global Hawk aircraft dropsondes measured surface winds as high as 54 kt, and recent satellite intensity estimates from TAFB and UW-CIMSS ADT are 60 kt and 57 kt, respectively. Based on these data, and given that Karl is now moving at a forward speed of at least 40 kt, the initial intensity has been conservatively increased to 60 kt. The initial motion estimate is now 055/40 kt. Karl should continue to move northeastward at 45-50 kt ahead of a broad deep-layer trough until the cyclone is absorbed by a larger extratropical low in about 36 hours. The new official forecast track is just an update of the previous advisory and remains near the middle of the tightly packed guidance envelope, close to the consensus model TVCN and the consensus of the GFS and ECMWF global models. Karl is currently located over a ridge of anomalously warm water with SSTs of 27C to 27.5C, which likely explains the unusually deep and cold-topped convection associated with the cyclone. Karl has about another 6 hours or so over SSTs greater than 26C, which could allow the cyclone to strengthen into a tropical hurricane before it reaches much colder waters. By 12 hours and beyond, Karl will be moving over sea-surface temperatures colder than 20C north of 40N latitude, which will result in the cyclone losing its deep convection and tropical characteristics. However, interaction with the aforementioned deep-layer trough and associated baroclinic energy should help Karl to strengthen into a powerful post-tropical low pressure system possessing hurricane-force winds. By 36 hours, the system should be absorbed into a larger extratropical low to its northwest. The new NHC intensity forecast and wind radii are based on input from the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 37.5N 53.5W 60 KT 70 MPH 12H 25/1800Z 41.3N 46.3W 70 KT 80 MPH...POST-TROPICAL 24H 26/0600Z 48.3N 35.5W 60 KT 70 MPH...POST-TROPICAL 36H 26/1800Z...ABSORBED BY LARGER EXTRATROPICAL LOW $$ Forecaster Stewart

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