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Tropical Storm MATTHEW Forecast Discussion Number 2

2016-09-28 22:43:35| National Hurricane Center (Atlantic)

Issued at 500 PM AST WED SEP 28 2016 000 WTNT44 KNHC 282043 TCDAT4 TROPICAL STORM MATTHEW DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142016 500 PM AST WED SEP 28 2016 Surface observations and aircraft data from earlier this afternoon indicate that the circulation of Matthew has continued to become better defined. There has also been an increase in convection just northeast of the center. The initial intensity remains 50 kt based on the earlier aircraft data. The next Air Force Reserve Hurricane Hunter mission into Matthew is scheduled for this evening. Although the increase in convection suggests that the system may be trying to establish an inner core, recent microwave and radar data have not revealed a significant increase in organization or banding so far. The aircraft also did not report any pressure fall during its mission. Based on these trends, little change in intensity is predicted in the short-range, but warm waters and low shear are expected to allow for steady strengthening while Matthew moves over the eastern and central Caribbean during the next few days. The updated NHC intensity forecast is a little below the intensity consensus through 24 hours, but is close to the consensus and the statistical models after that time. Matthew is moving westward to west-northwestward at about 16 kt. The track forecast reasoning is unchanged from the previous advisory. The tropical cyclone should move generally westward during the next 2 to 3 days to the south of a strong deep-layer ridge over the western Atlantic. The new NHC track forecast has been nudged northward through 72 hours, to be closer to the new model consensus. After day 3, Matthew is expected to turn northwestward as it nears the western portion of the ridge. The overall track envelope has shifted slightly eastward at days 4 and 5, and the NHC track has been adjusted accordingly. It should be noted that are still significant differences among the models in how soon and how sharply Matthew turns northwestward and northward late in the forecast period. Users are reminded that the average NHC track errors at days 4 and 5 are on the order of 180 and 240 miles, respectively. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 13.8N 62.0W 50 KT 60 MPH 12H 29/0600Z 14.1N 64.4W 50 KT 60 MPH 24H 29/1800Z 14.4N 67.1W 55 KT 65 MPH 36H 30/0600Z 14.4N 69.5W 65 KT 75 MPH 48H 30/1800Z 14.1N 71.3W 70 KT 80 MPH 72H 01/1800Z 14.2N 73.5W 80 KT 90 MPH 96H 02/1800Z 15.8N 75.0W 90 KT 105 MPH 120H 03/1800Z 19.0N 76.0W 90 KT 105 MPH $$ Forecaster Brown

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Tropical Storm ULIKA Forecast Discussion Number 10

2016-09-28 22:32:15| National Hurricane Center (East Pacific)

Issued at 200 PM PDT WED SEP 28 2016 000 WTPZ44 KNHC 282031 TCDEP4 TROPICAL STORM ULIKA DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192016 200 PM PDT WED SEP 28 2016 Ulika's cloud pattern consists of a small area of deep convection near the estimated center, with limited or no banding features. The current intensity estimate has been reduced to 50 kt which is a blend of Dvorak estimates from TAFB and SAB. Vertical shear, mainly due to westerly upper-level flow associated with a broad trough over the east-central Pacific, is predicted by the global models to increase substantially over the next couple of days. This, along with dry mid-tropospheric air, should cause steady weakening and Ulika is likely to degenerate into a post-tropical remnant low in 48 hours or less. Ulika is turning gradually to the left, and the initial motion is now estimated to be 010/6. As long as it maintains some vertical depth, the small circulation of the tropical cyclone should continue to rotate counter-clockwise around a mid-level low to its west. Assuming that the system becomes a shallow cyclone in 36 to 48 hours, it should move generally westward in the low-level flow by that time. The official forecast is very similar to the previous one and lies between the latest GFS and ECMWF predictions. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 15.1N 138.7W 50 KT 60 MPH 12H 29/0600Z 16.0N 138.9W 40 KT 45 MPH 24H 29/1800Z 16.9N 139.4W 35 KT 40 MPH 36H 30/0600Z 17.4N 140.2W 30 KT 35 MPH 48H 30/1800Z 17.6N 141.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 01/1800Z 17.7N 144.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 96H 02/1800Z...DISSIPATED $$ Forecaster Pasch/Kimberlain

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Tropical Storm ULIKA Forecast Discussion Number 9

2016-09-28 16:44:59| National Hurricane Center (East Pacific)

Issued at 800 AM PDT WED SEP 28 2016 000 WTPZ44 KNHC 281444 TCDEP4 TROPICAL STORM ULIKA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192016 800 AM PDT WED SEP 28 2016 Ulika was maintaining a small central dense overcast (CDO), with the center well embedded within this convective mass overnight. Since then, the cloud pattern has undergone considerable degradation. The CDO has become much less distinct, to the point that it has no longer become discernible. The deep convection in the former CDO has also decreased in coverage and cloud top temperatures have warmed substantially. TAFB and SAB provided a satellite classifications of T4.0 and T2.5 at 1200 UTC, respectively. Since that time, the cyclone's cloud pattern has further degraded, and the initial intensity is lowered to a possibly generous 60 kt. Ulika's environment already appears to have become much less favorable. West-southwesterly to southwesterly shear is only likely to increase as the cyclone gains latitude during the next couple of days. In fact, the SHIPS model output indicates more than 30 kt of shear by 36 hours. This, combined with a marginally moist environment and an increasingly convergent flow aloft, means that steady weakening is most likely. Global models show Ulika being sheared apart in about 2 days, with the mid-level center racing northeastward away from the low-level center. Rapid weakening should occur by then, if it has not begun already, and remnant low status is forecast in 72 hours. The new intensity forecast is lowered relative to the previous one, and is near or below the multi-model consensus. The initial motion is 030/06. Ulika should turn northward soon, as it rotates around a nearly stationary mid-tropospheric low seen in water vapor imagery around 17N 143W. Once the system decouples fully, the shallower cyclone's motion will be governed by the low-level trade wind flow and turn westward with an increase in forward speed. The new track forecast is a little to the right of the previous one through 24 hours and then is very similar, with the new forecast close to the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 14.5N 138.7W 60 KT 70 MPH 12H 29/0000Z 15.3N 138.6W 55 KT 65 MPH 24H 29/1200Z 16.0N 139.2W 50 KT 60 MPH 36H 30/0000Z 16.7N 140.1W 45 KT 50 MPH 48H 30/1200Z 17.3N 141.2W 35 KT 40 MPH 72H 01/1200Z 17.5N 144.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 02/1200Z 17.5N 148.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 03/1200Z...DISSIPATED $$ Forecaster Kimberlain

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Tropical Depression ROSLYN Forecast Discussion Number 13

2016-09-28 16:43:35| National Hurricane Center (East Pacific)

Issued at 800 AM PDT WED SEP 28 2016 000 WTPZ43 KNHC 281443 TCDEP3 TROPICAL DEPRESSION ROSLYN DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182016 800 AM PDT WED SEP 28 2016 Roslyn has been weakening. Deep convection associated with the cyclone dissipated late yesterday, and only a few puffs of new convection have redeveloped but are well removed to the northeast of the center. A TAFB Dvorak CI of 2.0 is used to lower the initial intensity to 30 kt, and assumes some spin-down of the vortex since the overnight ASCAT pass that showed 35-kt winds. With southwesterly shear of around 30 kt, increasing atmospheric stability and an extremely dry environment, and much cooler waters along the path of the cyclone, further weakening is likely. Roslyn is expected to degenerate into a remnant low later today, and the current intensity forecast is in good agreement with the guidance. The initial motion estimate is 035/09, though the shorter-term motion may be a bit more to the left. To the extent that Roslyn remains a coupled cyclone, the motion should gradually turn northward today around a cut-off low well southwest of the California coast. A turn toward the northwest is expected once the cyclone become a shallower feature, and its motion is governed by the low-level flow. The track forecast is essentially an update of the previous one and is close to a multi-model consensus without the GFDL model. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 21.0N 115.2W 30 KT 35 MPH 12H 29/0000Z 21.9N 115.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 29/1200Z 22.9N 116.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 30/0000Z 23.4N 116.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 30/1200Z 23.6N 117.6W 15 KT 15 MPH...POST-TROP/REMNT LOW 72H 01/1200Z...DISSIPATED $$ Forecaster Kimberlain

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Tropical Storm ROSLYN Forecast Discussion Number 12

2016-09-28 10:35:32| National Hurricane Center (East Pacific)

Issued at 200 AM PDT WED SEP 28 2016 000 WTPZ43 KNHC 280835 TCDEP3 TROPICAL STORM ROSLYN DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182016 200 AM PDT WED SEP 28 2016 The last bit of deep convection dissipated just after the release of the previous advisory, and all that is left is some shower activity displaced well to the northeast of Roslyn's center due to 30-35 kt of southwesterly shear. Recent ASCAT data indicate that the system is still producing a small area of tropical-storm-force winds in the southeastern quadrant, and the initial intensity remains 35 kt. Continued strong shear and cooler waters should cause the cyclone to gradually spin down during the next couple of days. Since it is unlikely that Roslyn will be able to reproduce organized deep convection, the cyclone is expected to degenerate to a remnant low later today. The global models all suggest that the remnant low will dissipate by day 3, if not sooner. The initial motion is north-northeastward, or 025/8 kt. Roslyn is expected to turn northward later today as it moves around a deep-layer trough extending southwestward from southern California. The shallow, convection-less remnant low should then turn northwestward and west-northwestward by 48 hours, steered by the low-level subtropical ridge. The new official track closely follows the TVCN multi-model consensus, which required an eastward shift from the previous track, primarily during the first 24 hours. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 20.2N 115.5W 35 KT 40 MPH 12H 28/1800Z 21.2N 115.6W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 29/0600Z 22.2N 116.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 29/1800Z 23.0N 117.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 30/0600Z 23.2N 117.8W 15 KT 15 MPH...POST-TROP/REMNT LOW 72H 01/0600Z...DISSIPATED $$ Forecaster Berg

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