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Tropical Depression EIGHT Forecast Discussion Number 1

2016-08-28 16:52:00| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT SUN AUG 28 2016 000 WTNT43 KNHC 281451 TCDAT3 TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082016 1100 AM EDT SUN AUG 28 2016 The area of low pressure located west of Bermuda has been producing intermittent organized deep convection for the last 24 hours or so, and the convection has increased markedly since 06Z. Given this, and the well-defined center shown by an overnight ASCAT pass, advisories are now being initiated on this system as a tropical cyclone. The initial intensity is estimated to be 30 kt based on the latest Dvorak estimates of T2.0/30 kt from TAFB and SAB. An Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate the depression this afternoon. The environment is only expected to be marginally conducive for intensification, with moderate southeasterly to easterly shear expected to become southwesterly and increase further in 36 to 48 hours. As a result, only modest strengthening is shown in the official forecast, with the depression expected to become a tropical storm in the next day or two. After that time, the global models show the cyclone opening up along a frontal zone well offshore of the northeastern United States. However, there is some disagreement in when this will occur, with the GFS showing the cyclone dissipating in about 3 days, and the ECMWF hanging onto it until around day 5. As a compromise, the NHC forecast shows dissipation after day 4, but this timing is quite uncertain. The depression is currently situated south of a mid-level ridge that extends from the Mid-Atlantic states into the western Atlantic, and the initial motion estimate is 280/08. The ridge is forecast to break down and shift eastward during the next 2-3 days, which should result in the cyclone gradually turning poleward and then recurving during the next 72 hours. The NHC track forecast is close to a blend of the GFS and ECMWF models through dissipation. This forecast keeps the center of the cyclone east of the Outer Banks of North Carolina, but a tropical storm watch may be needed for that area later today. Based on an evaluation of satellite imagery and data during the past few days, it appears that the remnants of Tropical Storm Fiona are not directly responsible for the genesis of this depression. The Fiona remnants were absorbed into a separate area of pre-existing vorticity, with the current depression developing out of the combined system. As a result, this is considered to be a new tropical cyclone, not a regeneration of a previous tropical cyclone. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 31.5N 70.0W 30 KT 35 MPH 12H 29/0000Z 32.1N 71.6W 30 KT 35 MPH 24H 29/1200Z 32.9N 73.3W 30 KT 35 MPH 36H 30/0000Z 33.6N 74.4W 35 KT 40 MPH 48H 30/1200Z 34.2N 75.0W 35 KT 40 MPH 72H 31/1200Z 36.5N 73.0W 35 KT 40 MPH 96H 01/1200Z 39.0N 66.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 02/1200Z...DISSIPATED $$ Forecaster Brennan

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Hurricane LESTER Forecast Discussion Number 16

2016-08-28 16:34:40| National Hurricane Center (East Pacific)

Issued at 800 AM PDT SUN AUG 28 2016 000 WTPZ43 KNHC 281434 TCDEP3 HURRICANE LESTER DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132016 800 AM PDT SUN AUG 28 2016 The cloud pattern has continued to deteriorate and the eye is no longer observed on conventional imagery, but it is hidden under the cirrus canopy as revealed by a 1206 UTC SSMIS pass. The convection continues to be concentrated near the center, and the outflow is fair. Dvorak objective numbers from CIMMS and estimates from TAFB and SAB support a lower intensity of 75 kt. There are no obvious reasons why Lester should continue to weaken. The environment, at least for the next few days, does not appear to be detrimental for Lester to intensify, other than perhaps a small decrease in the SSTs. Given these factors, the NHC forecast calls for no change in intensity during the next 4 days with some weakening thereafter when Lester eventually encounters drier air. This forecast is consistent with the intensity consensus model. Lester is moving toward the west or 270 degrees at 11 kt. The track forecast is a little more straightforward since the hurricane is embedded within a deep layer of easterly flow associated with a persistent subtropical ridge across the Pacific. By the end of the forecast period, Lester will likely turn west-northwest toward a weakness inf the ridge. Track guidance is tightly packed, and the NHC forecast is very close to the multi-model consensus, and does not deviate much from the previous NHC prediction FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 18.1N 123.7W 75 KT 85 MPH 12H 29/0000Z 18.2N 125.7W 75 KT 85 MPH 24H 29/1200Z 18.3N 128.5W 75 KT 85 MPH 36H 30/0000Z 18.5N 131.2W 75 KT 85 MPH 48H 30/1200Z 18.5N 134.0W 75 KT 85 MPH 72H 31/1200Z 18.5N 138.8W 75 KT 85 MPH 96H 01/1200Z 18.5N 143.0W 75 KT 85 MPH 120H 02/1200Z 19.5N 148.0W 70 KT 80 MPH $$ Forecaster Avila

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Hurricane LESTER Forecast Discussion Number 15

2016-08-28 10:43:26| National Hurricane Center (East Pacific)

Issued at 200 AM PDT SUN AUG 28 2016 000 WTPZ43 KNHC 280843 TCDEP3 HURRICANE LESTER DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132016 200 AM PDT SUN AUG 28 2016 Lester's cloud pattern is not as well organized as it was late yesterday. The distribution of deep convection within the hurricane's central dense overcast has become asymmetric and an eye is no longer visible. Despite Lester's degraded appearance in conventional satellite imagery, microwave data from several hours ago suggested that Lester was generally maintaining its inner-core structure. Dvorak T-numbers have decreased since the last advisory. A blend of Final T- and CI-numbers from both satellite agencies supports lowering the initial intensity estimate to 85 kt. The initial motion estimate is 270/12. A strong subtropical ridge should steer Lester just north of due-west for the next 3 to 4 days. Longer term, uncertainty regarding the strength of the subtropical ridge north of Lester and any potential binary interaction with Madeline come into play. This uncertainty seems to be less than in previous cycles, however, with the GFS and ECMWF now much closer at 96 and 120 hours. The new NHC track is close to a blend of these two models throughout the forecast period and is just a bit to the south of the previous forecast at those times. It is not clear what interrupted Lester's intensification. Regardless, Lester should be in a low-shear, marginally moist environment and over only gradually decreasing sea surface temperatures during the next few days. Assuming that the hurricane continues to retain its inner-core structure, this could allow Lester to re-intensify some during the next 12 to 24 hours before it encounters even drier mid-level air. However, none of the intensity guidance shows this possibility, and instead shows slow weakening for the remainder of the forecast period. The intensity forecast is a challenging one, and is of overall low confidence. It shows little change in strength in the short term and is slightly above the consensus aids, but is then near the multi-model consensus after that. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 17.9N 122.2W 85 KT 100 MPH 12H 28/1800Z 17.9N 124.1W 85 KT 100 MPH 24H 29/0600Z 18.1N 126.9W 85 KT 100 MPH 36H 29/1800Z 18.2N 129.7W 80 KT 90 MPH 48H 30/0600Z 18.4N 132.3W 75 KT 85 MPH 72H 31/0600Z 18.4N 137.4W 75 KT 85 MPH 96H 01/0600Z 18.6N 142.2W 75 KT 85 MPH 120H 02/0600Z 19.4N 147.1W 70 KT 80 MPH $$ Forecaster Kimberlain

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Hurricane GASTON Forecast Discussion Number 22

2016-08-28 04:54:53| National Hurricane Center (Atlantic)

Issued at 1100 PM AST SAT AUG 27 2016 000 WTNT42 KNHC 280254 TCDAT2 HURRICANE GASTON DISCUSSION NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 1100 PM AST SAT AUG 27 2016 Gaston has become a hurricane again with a well-defined eye on microwave images that has been occasionally showing up on conventional satellite pictures. Dvorak estimates are T4.5/77 kt from both TAFB and SAB, so the initial wind speed is increased to 75 kt. The environment near Gaston, other than some dry mid-level air, looks conducive for strengthening for the next day or so. While the environment doesn't change much in the next couple of days overall, Gaston is expected to move very slowly, which could upwell some cooler water. Thus the wind speed forecast will be leveled off after 24 hours. A more consistent weakening trend is expected beyond 72 hours when the cyclone moves over colder waters and experiences stronger shear. The latest NHC prediction is higher than the previous one, mostly owing to the initial conditions, and is close to a blend of the FSU Superensemble and the intensity consensus. Satellite fixes show that Gaston is moving slower to the northwest, at about 7 kt. The storm should continue to decelerate over the next day or so as it reaches a break in the subtropical ridge, and have a slow motion to the north or northeast from 24 to 48 hours. The next shortwave trough in the mid-latitude is forecast to reach Gaston in about 3 days, which will likely cause the hurricane to recurve to the east-northeast, albeit at a slower rate of speed than you normally see over the North Atlantic. Guidance has not changed much since the last cycle, and the official forecast is basically an update of the previous one, a bit slower than the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 29.6N 54.2W 75 KT 85 MPH 12H 28/1200Z 30.1N 54.7W 85 KT 100 MPH 24H 29/0000Z 30.7N 55.1W 95 KT 110 MPH 36H 29/1200Z 31.0N 55.2W 95 KT 110 MPH 48H 30/0000Z 31.4N 54.8W 90 KT 105 MPH 72H 31/0000Z 32.6N 52.2W 90 KT 105 MPH 96H 01/0000Z 34.6N 48.1W 85 KT 100 MPH 120H 02/0000Z 37.5N 42.0W 70 KT 80 MPH $$ Forecaster Blake

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Hurricane LESTER Forecast Discussion Number 14

2016-08-28 04:50:21| National Hurricane Center (East Pacific)

Issued at 800 PM PDT SAT AUG 27 2016 000 WTPZ43 KNHC 280250 TCDEP3 HURRICANE LESTER DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132016 800 PM PDT SAT AUG 27 2016 Lester has gone through some impressive changes this evening. The well-developed eye has disappeared during the past couple of hours on satellite images, with decreasing convection noted in the eastern eyewall. A blend of the Dvorak estimates from all agencies supported increasing the winds to 95 kt at the synoptic time, but I have elected to show an initial wind speed of 90 kt given the recent degradation on satellite. The hurricane should be in a low-shear, marginal-moisture environment for the next several days, with only gradually decreasing water temperatures expected as Lester moves nearly parallel to the typical eastern Pacific SST gradient. Most of the guidance suggest that Lester's intensity will peak within the next 24 hours, then slowly fall. This is a trickier forecast than it seems because the forecast environmental conditions are reminiscent of those necessary for an annular hurricane, which would likely keep Lester stronger than much of the guidance. At this point, given the recent satellite trends, the official intensity prediction is kept the same as the previous one, a bit higher than the intensity consensus. The initial motion estimate remains 270/11. A strong subtropical ridge to the north of Lester should steer the cyclone on a westward course for at least the next 3 to 4 days. After that time, uncertainties increase with both the strength of the ridge and any potential binary interaction with Madeline. There have been very little changes to the overall guidance suite, and the new NHC track forecast is near the previous one, nudged a bit to the west at longer ranges. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 18.0N 120.8W 90 KT 105 MPH 12H 28/1200Z 18.1N 122.6W 95 KT 110 MPH 24H 29/0000Z 18.2N 125.4W 95 KT 110 MPH 36H 29/1200Z 18.3N 128.3W 90 KT 105 MPH 48H 30/0000Z 18.4N 131.0W 85 KT 100 MPH 72H 31/0000Z 18.6N 136.0W 80 KT 90 MPH 96H 01/0000Z 18.7N 140.9W 75 KT 85 MPH 120H 02/0000Z 19.5N 145.5W 70 KT 80 MPH $$ Forecaster Blake

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