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Hurricane ORLENE Forecast Discussion Number 10

2016-09-13 10:45:44| National Hurricane Center (East Pacific)

Issued at 200 AM PDT TUE SEP 13 2016 000 WTPZ41 KNHC 130845 TCDEP1 HURRICANE ORLENE DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162016 200 AM PDT TUE SEP 13 2016 Recent microwave images suggest that there has been some erosion of the southern portion of the eyewall overnight, and the overall satellite presentation of the hurricane has continued to gradually degrade. The eye has become cloud filled in infrared satellite pictures and the convective tops surrounding the eye have warmed overnight. Despite the recent loss of organization, a blend of the subjective and objective Dvorak T- and CI-numbers yields an initial intensity estimate of 90 kt. The leveling-off of Orlene's intensity appears to have been caused by 15-20 kt of south-southwesterly shear as diagnosed by a UW/CIMSS shear analysis. The shear conditions are not expected to change much today. Meanwhile, Orlene is forecast to move very slowly during the next 36 h, which is likely to cause upwelling of cooler waters. These conditions are expected to cause gradual weakening during the next day or so. After that time, the shear is expected to decrease, but less favorable thermodynamic conditions are likely to continue to contribute to weakening. The new NHC intensity forecast shows a little more weakening during the next 2-3 days, but is close to the previous advisory thereafter. This is in good agreement with the latest Florida State Superensemble and close to the IVCN consensus model. It appears that the hurricane is beginning to slow down as anticipated, with an estimated initial motion of 360/4 kt. Orlene will be within an area of light steering currents during the next day or so, and only a slow northward motion is anticipated today. By Wednesday, a subtropical ridge to the north of the hurricane is forecast to strengthen, which should begin to steer Orlene westward at a faster rate of speed. Near the end of the forecast period, the models begin to diverge, with the latest GFS now taking a stronger system more poleward, while the ECMWF shows a weaker Orlene moving more westward. Since this is a flip-flop in the models from the previous runs, the NHC track maintains the more westward solution, and is close to the GFS ensemble mean and the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 19.2N 118.9W 90 KT 105 MPH 12H 13/1800Z 19.7N 118.9W 80 KT 90 MPH 24H 14/0600Z 20.1N 119.0W 70 KT 80 MPH 36H 14/1800Z 20.2N 119.7W 60 KT 70 MPH 48H 15/0600Z 20.2N 121.1W 55 KT 65 MPH 72H 16/0600Z 19.9N 125.6W 45 KT 50 MPH 96H 17/0600Z 19.7N 130.5W 45 KT 50 MPH 120H 18/0600Z 20.0N 134.3W 40 KT 45 MPH $$ Forecaster Brown

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Tropical Storm IAN Forecast Discussion Number 4

2016-09-13 10:42:43| National Hurricane Center (Atlantic)

Issued at 500 AM AST TUE SEP 13 2016 000 WTNT45 KNHC 130842 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 500 AM AST TUE SEP 13 2016 Ian is a strongly sheared tropical storm. The low-level center of the cyclone is completely exposed with the main area of deep convection located about 120 n mi northeast of the center. This asymmetric cloud pattern is the result of about 30 kt of southwesterly vertical wind shear. The initial intensity is held at 40 kt for this advisory, in agreement with the earlier ASCAT data. This estimate is a little higher than the latest Dvorak classifications. Satellite fixes indicate that Ian has slowed down during the last several hours. The initial motion estimate, using a 12-h average, is 335/8 kt. The tropical cyclone is situated between a mid- to upper-level low to its west and a mid-level high to its east. This pattern is expected to persist for the next couple of days, and should cause Ian to move north-northwestward to northward with a slight increase in forward speed. After that time, a shortwave trough is expected to approach the tropical storm, and it will likely cause Ian to turn northeastward and accelerate as it becomes embedded in the mid-latitude flow. The models are in fair agreement in this overall scenario, and only small changes were made to the previous NHC track forecast. This prediction is in best agreement with the various consensus aids. The strong shear currently affecting Ian is expected to persist for another 24 hours, so little change in strength is predicted during that time. The shear is forecast to lessen some in a couple of days while Ian is still over warm water. These environmental conditions, combined with some baroclinic forcing, could allow for slight strengthening in the 36- to 72-h time period. After that time, Ian is expected to move back into a strong shear environment and over progressively colder water, which should lead to extratropical transition in about 4 days. The NHC intensity forecast is largely the same as the previous one, and is in best agreement with the SHIPS guidance during its tropical phase and the global models during the extratropical portion. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 24.0N 51.7W 40 KT 45 MPH 12H 13/1800Z 25.4N 52.5W 40 KT 45 MPH 24H 14/0600Z 27.8N 53.4W 40 KT 45 MPH 36H 14/1800Z 30.4N 53.8W 45 KT 50 MPH 48H 15/0600Z 33.2N 53.1W 50 KT 60 MPH 72H 16/0600Z 40.7N 46.1W 50 KT 60 MPH 96H 17/0600Z 50.7N 32.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 18/0600Z 58.5N 18.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi

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Hurricane ORLENE Forecast Discussion Number 9

2016-09-13 04:49:17| National Hurricane Center (East Pacific)

Issued at 800 PM PDT MON SEP 12 2016 000 WTPZ41 KNHC 130249 TCDEP1 HURRICANE ORLENE DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162016 800 PM PDT MON SEP 12 2016 Orlene's rapid intensification episode has been interrupted. Satellite imagery indicates some erosion of the cyclone's deep convection, primarily over the northeastern quadrant of the circulation. The eye has also become cloud-filled and indistinct. A 2324 UTC SSM/I overpass suggested that an eyewall replacement is underway, which could be the reason for the cyclone's somewhat degraded satellite appearance. The latest satellite classification from TAFB was T4.5/77kt and the UW-CIMSS ADT is around that value. A blend of these data with Dvorak CI-numbers yields an initial intensity estimate of 90 kt. Orlene has wobbled a little east of due north during the last several hours, but an estimate of the cyclone's longer-term initial motion estimate is 360/05. The hurricane is about to enter a col region, which should result in a northward or north-northwestward drift during the next 24 hours or so. The subtropical ridge is expected to re-strengthen in about 2 days, causing Orlene to turn south of due west with a substantial increase in forward speed. By 120 hours, the model spread begins to widen, with the ECMWF farther north and slower compared to the faster and more southern GFS. This difference arises due to the models' handling of a strong mid- to upper-tropospheric cyclone around 140W. The ECMWF shows this feature farther south and stronger while the GFS maintains the subtropical ridge north of Orlene. The NHC track forecast is not much different than the previous one, but a little slower by day 5 as a result of the increasing track uncertainty. With an eyewall replacement in progress, Orlene should continue to slowly weaken. The cyclone will likely not be able to recover either since it should come to a halt over a region where the oceanic heat content rapidly drops off. Orlene's slow motion should induce significant oceanic upwelling, which could accelerate the rate of weakening during the next day or two. After that time, the cyclone will encounter an environment of critically low moisture, which should promote additional slow weakening. The new NHC intensity forecast is reduced relative to the previous one and is near the latest multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 18.7N 119.1W 90 KT 105 MPH 12H 13/1200Z 19.2N 119.1W 90 KT 105 MPH 24H 14/0000Z 19.7N 119.2W 80 KT 90 MPH 36H 14/1200Z 19.9N 119.7W 70 KT 80 MPH 48H 15/0000Z 19.8N 120.9W 60 KT 70 MPH 72H 16/0000Z 19.3N 125.0W 50 KT 60 MPH 96H 17/0000Z 18.9N 130.2W 45 KT 50 MPH 120H 18/0000Z 19.0N 133.7W 40 KT 45 MPH $$ Forecaster Kimberlain

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Tropical Storm IAN Forecast Discussion Number 3

2016-09-13 04:42:44| National Hurricane Center (Atlantic)

Issued at 1100 PM AST MON SEP 12 2016 000 WTNT45 KNHC 130242 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 1100 PM AST MON SEP 12 2016 Ian remains a sheared tropical cyclone, with the strongest convection displaced to the northeast and east of the center. However, moderate convection has recently developed over and just north of the center due to the vertical wind shear's backing from a southwesterly to southerly direction. Data from a recent partial ASCAT-B overpass indicate that the 34-kt wind field has expanded to at least 200 nmi in the northeastern quadrant, and that peak winds have also increased to more than 35 kt. Dvorak satellite intensity estimates are T3.0/45 kt from TAFB and T2.5/35 kt from SAB, and an average of these values yields an advisory intensity of 40 kt. Ian has maintained a steady motion of 330/11 kt. The latest NHC model guidance is in excellent agreement on the storm continuing to move north-northwestward through a break in the Bermuda-Azores High for the next 24 hours, followed by a turn to the north at 36-48 hours. After that, Ian is expected to gradually accelerate as the cyclone gets captured by a strong mid-latitude shortwave trough. The new official forecast track is essentially just an update of the previous advisory track and lies close to the GFS-ECMWF model consensus, and the multi-model consensus TVCN. The vertical shear is forecast to decrease to 15-20 kt in 36 to 48 hours when an upper-level low, currently located about 400 nmi northwest of the cyclone, is forecast by the GFS, UKMET, and ECMWF models to move over and become colocated with Ian's low-level center. The combination of decreasing vertical wind shear and some infusion of baroclinic energy associated with this complex interaction is expected to produce at least some slight strengthening by days 2-3. Around 120 hours, Ian is forecast to interact with a frontal zone over the north Atlantic and be transformed into an extratropical cyclone. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 23.5N 51.5W 40 KT 45 MPH 12H 13/1200Z 24.9N 52.4W 40 KT 45 MPH 24H 14/0000Z 26.9N 53.4W 40 KT 45 MPH 36H 14/1200Z 29.4N 54.1W 45 KT 50 MPH 48H 15/0000Z 31.8N 54.0W 50 KT 60 MPH 72H 16/0000Z 38.0N 49.7W 50 KT 60 MPH 96H 17/0000Z 48.0N 38.0W 50 KT 60 MPH 120H 18/0000Z 56.5N 25.2W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Tropical Storm IAN Forecast Discussion Number 2

2016-09-12 22:42:11| National Hurricane Center (Atlantic)

Issued at 500 PM AST MON SEP 12 2016 000 WTNT45 KNHC 122042 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 500 PM AST MON SEP 12 2016 Ian remains poorly organized, with the bulk of the deep convection displaced well to the northeast of the low-level center due to strong vertical shear. The advisory intensity estimate remains at 35 kt in agreement with a Dvorak estimate from TAFB. The global models suggest that some decrease in shear will occur in 36 to 48 hours, when the system moves on the northeast side of a partially cut off upper-level cyclone. This could permit a little strengthening to commence around that time, as reflected in the official forecast. This is slightly above the latest numerical model intensity consensus. By the end of the forecast period, or sooner, Ian should become embedded in a frontal zone over the north Atlantic and be transformed into an extratropical cyclone. Ian has turned to the right, and the initial motion estimate is now about 330/11 kt. The storm continues to move through a break in the subtropical ridge, and in a few days the flow ahead of a mid-tropospheric trough should cause Ian to accelerate north-northeastward to northeastward. The official forecast lies between the latest GFS and ECMWF predictions, and is also close to the dynamical model consensus. FORECAST POSITIONS AND MAX WINDS INIT 12/2100Z 22.9N 50.7W 35 KT 40 MPH 12H 13/0600Z 24.3N 51.7W 35 KT 40 MPH 24H 13/1800Z 26.2N 52.9W 35 KT 40 MPH 36H 14/0600Z 28.5N 54.0W 40 KT 45 MPH 48H 14/1800Z 30.7N 54.5W 45 KT 50 MPH 72H 15/1800Z 35.7N 52.4W 50 KT 60 MPH 96H 16/1800Z 45.0N 42.0W 50 KT 60 MPH 120H 17/1800Z 54.5N 29.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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