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Tropical Storm FRED Forecast Discussion Number 26
2015-09-05 10:34:34| National Hurricane Center (Atlantic)
Issued at 500 AM AST SAT SEP 05 2015 000 WTNT41 KNHC 050834 TCDAT1 TROPICAL STORM FRED DISCUSSION NUMBER 26 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062015 500 AM AST SAT SEP 05 2015 Fred continues to produce bursts of convection, although the bursts are smaller and farther from the center than they were 24 hours ago. This suggests that the ongoing 35-40 kt of westerly vertical shear is causing a gradual weakening. The initial intensity remains 35 kt based on a subjective satellite intensity estimate from TAFB, as well as objective AMSU and satellite consensus estimates from CIMSS and CIRA. The central pressure has been lowered a little based on additional observations from drifting buoy 13519, which reported a minimum pressure of 1008.4 mb as the center of Fred passed to the north. The initial motion is 290/10. Fred is approaching a large break in the subtropical ridge caused by a mid- to upper-level trough and associated surface low centered several hundred miles east of Bermuda. The track guidance is in good agreement that this baroclinic system will move eastward for the next several days, with Fred recurving to the northeast between it and the subtropical ridge. After recurvature, there is some spread in the forecast forward speed, with the new track compromising between the faster ECMWF/GFS models and the slower UKMET/Canadian models. The new track is nudged slightly to the north of the previous track from 36-96 hours, and then is nudged a little to the east of the previous track at 120 hours. The intensity forecast is low in confidence due to several possible scenarios. First, although it is not explicitly forecast, Fred could become a remnant low at any time during the next 24 to 36 hours due to continued shear and dry air entrainment, followed by regeneration to a tropical cyclone when the shear subsequently decreases. Second, the dynamical models have two scenarios for Fred as it interacts with the above-mentioned trough and surface low after recurvature. One possibility, supported by the GFS and the ECMWF, is that a relatively weak Fred gets absorbed into the baroclinic low and dissipates earlier than currently forecast. Another possibility, supported by the UKMET and Canadian models, is that Fred stays farther away from the baroclinic low and intensifies more than is currently forecast. Given the uncertainty, the new intensity forecast is similar to the previous forecast in calling for slight weakening early in the forecast period followed by slight intensification after 36 hours. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 23.2N 41.0W 35 KT 40 MPH 12H 05/1800Z 23.7N 42.1W 30 KT 35 MPH 24H 06/0600Z 24.7N 42.7W 30 KT 35 MPH 36H 06/1800Z 26.3N 42.5W 30 KT 35 MPH 48H 07/0600Z 28.2N 41.1W 35 KT 40 MPH 72H 08/0600Z 31.5N 37.5W 35 KT 40 MPH 96H 09/0600Z 35.0N 33.0W 35 KT 40 MPH 120H 10/0600Z 36.5N 30.0W 35 KT 40 MPH $$ Forecaster Beven
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fred
Tropical Storm KEVIN Forecast Discussion Number 18
2015-09-05 04:44:59| National Hurricane Center (East Pacific)
Issued at 800 PM PDT FRI SEP 04 2015 000 WTPZ44 KNHC 050244 TCDEP4 TROPICAL STORM KEVIN DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142015 800 PM PDT FRI SEP 04 2015 Satellite images indicate that the area of convection on the north side of Kevin continues to move farther away from the apparent center. The low-level circulation also appeared to be elongating from north to south on the last light visible imagery, with a recent microwave pass confirming that degraded structure. A blend of Dvorak estimates supports lowering the intensity to 40 kt. Remnant low status is expected by 36 hours, with the circulation probably degenerating into a trough by day 3. The center is getting harder to track, but I don't see convincing evidence that the initial motion has changed from the previous advisory, so it will remain 360/07. A leftward turn should occur overnight due to the cyclone decoupling from its mid-level center and being steered more by the low-level flow. The shallower cyclone should then gain a greater westerly component of motion this weekend as it moves around the low-level subtropical ridge over the eastern Pacific. The new track forecast is basically just an update of the previous one, and is south of the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 22.7N 115.2W 40 KT 45 MPH 12H 05/1200Z 23.4N 115.6W 35 KT 40 MPH 24H 06/0000Z 23.9N 116.4W 25 KT 30 MPH 36H 06/1200Z 24.1N 117.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 07/0000Z 24.2N 118.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 08/0000Z...DISSIPATED $$ Forecaster Blake
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kevin
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Tropical Depression FRED Forecast Discussion Number 24
2015-09-04 22:33:29| National Hurricane Center (Atlantic)
Issued at 500 PM AST FRI SEP 04 2015 000 WTNT41 KNHC 042033 TCDAT1 TROPICAL DEPRESSION FRED DISCUSSION NUMBER 24 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062015 500 PM AST FRI SEP 04 2015 The depression consists of a very tight circulation largely devoid of deep convection. Recently a convective band is forming east of the center, but it appears that each new burst of convection is weaker than the previous one. It is estimated that the winds are still 30 kt, and given the strong shear the NHC forecast calls for Fred to become a remnant low in 24 hours or so. The GFS and UK global models, as well as the SHIPS/GFS and SHIPS/ECMWF intensity guidance, regenerate Fred by the end of the forecast period, and so does the official forecast. The steering pattern has not changed yet, and the depression is still moving on a general west to west-northwest track at 8 kt. In about 48 hours, a strong mid-latitude trough is forecast by the global models to deepen in the central Atlantic. This pattern should force the depression or its remnants to recurve and become embedded within the mid-latitude westerly flow. The NHC forecast is within the guidance envelope during the next 2 to 3 days and then lies between the GFS and the multi-model consensus. The GFS insists on keeping Fred meandering across the North Atlantic for more than a week. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 22.6N 39.1W 30 KT 35 MPH 12H 05/0600Z 22.8N 40.2W 30 KT 35 MPH 24H 05/1800Z 23.3N 41.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 06/0600Z 24.0N 42.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 06/1800Z 25.5N 42.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 07/1800Z 28.5N 39.5W 30 KT 35 MPH...TROPICAL DEPRESSION 96H 08/1800Z 31.5N 35.5W 30 KT 35 MPH...TROPICAL DEPRESSION 120H 09/1800Z 33.5N 31.5W 30 KT 35 MPH...TROPICAL DEPRESSION $$ Forecaster Avila
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tropical
Tropical Storm KEVIN Forecast Discussion Number 16
2015-09-04 16:54:30| National Hurricane Center (East Pacific)
Issued at 800 AM PDT FRI SEP 04 2015 000 WTPZ44 KNHC 041454 TCDEP4 TROPICAL STORM KEVIN DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142015 800 AM PDT FRI SEP 04 2015 Kevin's cloud pattern consists of a large circular mass of very deep convection, with the low- to mid-level centers nearly co-located as of several hours. Since that time, satellite data indicate that the cyclone has begun the process of decoupling due to the 25 kt of south-southwesterly vertical shear affecting it. Although Dvorak intensity estimates were T3.5/55 kt from TAFB and SAB at 1200 UTC, the initial wind speed is kept at 50 kt due to the weakening that has likely begun. Even stronger shear associated with a potent mid- to upper-level trough to the northwest of Kevin should result in a complete separation of the cyclone's low- to mid-level circulations within 24 hours, according to global models. Substantially drier air behind the trough should also be entrained by the cyclone, which should cause a collapse of deep convection during the next or so. Global models depict Kevin becoming a remnant low in about 36 hours and show dissipation by 72 hours. The new intensity forecast shows faster weakening than the previous one, with remnant low status and dissipation also indicated sooner. Based on fixes from a series of microwave passes overnight, the cyclone has been moving a little east of due north, and the initial motion estimate is 010/07. Kevin should turn due north soon when the trough to its northwest sinks southward. As Kevin decouples during the next 24 hours, a deceleration is forecast by the model guidance. A bend in the track toward the northwest and west- northwest is also anticipated during this time, when Kevin meets the opposing flow around the low-level subtropical ridge over the eastern Pacific. The new track forecast is on the right side of the guidance envelope at first, primarily due to the north-northeasterly motion overnight but is shifted a bit southward once Kevin becomes a remnant low. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 21.2N 115.2W 50 KT 60 MPH 12H 05/0000Z 22.1N 115.4W 45 KT 50 MPH 24H 05/1200Z 22.9N 116.0W 35 KT 40 MPH 36H 06/0000Z 23.3N 116.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 06/1200Z 23.4N 118.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 07/1200Z...DISSIPATED $$ Forecaster Kimberlain
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Tropical Depression FRED Forecast Discussion Number 23
2015-09-04 16:46:58| National Hurricane Center (Atlantic)
Issued at 1100 AM AST FRI SEP 04 2015 000 WTNT41 KNHC 041446 TCDAT1 TROPICAL DEPRESSION FRED DISCUSSION NUMBER 23 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062015 1100 AM AST FRI SEP 04 2015 Fred consists of a tight swirl of low clouds with intermittent bursts of deep convection. There has been no scatterometer data over the cyclone for several hours, but it appears that the circulation is not as vigorous as it was yesterday. Dvorak T-numbers are gradually decreasing, and on this basis, the initial intensity has been lowered to 30 kt. The shear is forecast to remain high during the next 48 hours or so, resulting in additional weakening. Fred is expected to become a remnant low tonight or Saturday, however, most of the global models suggest that the shear near the system could relax in 3 days. If Fred still exists by then, and given that the ocean is anomalously warm in the North Atlantic, there is a chance of regeneration. This would likely occur after Fred or its remnants recurve into the mid-latitude westerlies. The depression is moving toward the west or 280 degrees at 9 kt, steered by a subtropical high to its north. A strong mid-latitude trough is forecast by the global models to deepen in the central Atlantic during the next 2 days, and this pattern will force Fred to recurve northeastward. This is indicated in the NHC forecast, which follows the reliable dynamical guidance very closely. It is interesting to note that the GFS global model in the past couple of runs keeps Fred lingering across the North Atlantic for more than a week. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 22.3N 38.3W 30 KT 35 MPH 12H 05/0000Z 22.6N 39.6W 30 KT 35 MPH 24H 05/1200Z 23.0N 41.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 06/0000Z 24.0N 42.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 06/1200Z 25.0N 42.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 07/1200Z 28.0N 40.0W 30 KT 35 MPH...TROPICAL DEPRESSION 96H 08/1200Z 30.5N 36.0W 30 KT 35 MPH...TROPICAL DEPRESSION 120H 09/1200Z 34.0N 31.0W 30 KT 35 MPH...TROPICAL DEPRESSION $$ Forecaster Avila
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