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Tropical Storm IAN Forecast Discussion Number 1

2016-09-12 16:43:07| National Hurricane Center (Atlantic)

Issued at 1100 AM AST MON SEP 12 2016 000 WTNT45 KNHC 121443 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 1100 AM AST MON SEP 12 2016 Visible satellite images and a recent ASCAT overpass show that the low pressure system over the central Atlantic has now acquired a well-defined low-level circulation. The scatterometer data showed tropical-storm-force winds over the northern semicircle of the circulation, and the advisory intensity is set to 35 kt. Ian is not a well organized storm, with the low-level center exposed and displaced about 70 n mi to the southwest of the main area of deep convection. This is due to the effect of about 20 kt of vertical shear over the system, and this strong shear is predicted to persist for at least the next day or so. In 36 to 48 hours, the shear is forecast to relax somewhat, so some slow intensification could begin by tomorrow night. The official intensity forecast is a little above the model consensus. In 120 hours, or sooner, the system should become embedded within a frontal zone over north Atlantic and lose tropical characteristics. Ian is moving northwestward, with initial motion estimated to be about 320/11 kt. The storm is currently moving through a break in the subtropical ridge. In the next few days, a 500 mb trough approaching from the west should cause Ian to turn northward and then north-northeastward while accelerating. The official forecast track leans toward the ECMWF solution, but is also not far from the latest dynamical model consensus. FORECAST POSITIONS AND MAX WINDS INIT 12/1500Z 21.8N 50.4W 35 KT 40 MPH 12H 13/0000Z 23.4N 51.2W 35 KT 40 MPH 24H 13/1200Z 25.4N 52.4W 35 KT 40 MPH 36H 14/0000Z 27.3N 53.6W 40 KT 45 MPH 48H 14/1200Z 29.7N 54.8W 45 KT 50 MPH 72H 15/1200Z 34.5N 53.8W 50 KT 60 MPH 96H 16/1200Z 42.5N 45.5W 50 KT 60 MPH 120H 17/1200Z 53.0N 32.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Hurricane ORLENE Forecast Discussion Number 6

2016-09-12 10:39:09| National Hurricane Center (East Pacific)

Issued at 200 AM PDT MON SEP 12 2016 000 WTPZ41 KNHC 120839 TCDEP1 HURRICANE ORLENE DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162016 200 AM PDT MON SEP 12 2016 Orlene continues to strength. Satellite images indicate that the relatively compact tropical cyclone has become better organized since the previous advisory with an eye occasionally evident in infrared images. Recent microwave data also indicate that the inner core of the cyclone is better defined. Dvorak classifications from TAFB and SAB were 4.0/65 kt and 4.5/77 kt, respectively, and automated values from CIMSS at the University of Wisconsin are 4.4/75 kt. Based on these data, the initial wind speed is increased to 70 kt, making Orlene a category 1 hurricane on the Saffir-Simpson Hurricane Wind Scale. Orlene has strengthened at a rapid rate of 35 kt during the past 24 hours. The hurricane is moving northwestward, or 305 degrees, at 8 kt. A trough over the U.S. Pacific northwest is expected to dig southward during the next day or two, causing a significant weakness in the subtropical ridge. This pattern change should cause Orlene to turn northwestward or northward and slow down later today, and the cyclone will likely come to a crawl in the 24-48-hour time period. Beyond that time, the trough is expected to lift out allowing ridging to become re-established to the north of the system. This should result in Orlene moving westward at a faster pace. The models are in good agreement on this scenario, and the NHC track forecast is largely an update of the previous one. Additional strengthening seems likely during the next 24 hours while the hurricane remains over warm water, and in an environment of low wind shear and relatively moist conditions. After that time, a slow weakening should commence due to decreasing relative humidity values and cooler water temperatures, likely aided by cold water upwelling. The NHC intensity forecast is near the high end of the models, in best agreement with the LGEM and Florida State Superensemble guidance, and is slightly higher than the previous one in the short term. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 17.1N 119.1W 70 KT 80 MPH 12H 12/1800Z 17.7N 119.5W 80 KT 90 MPH 24H 13/0600Z 18.5N 119.7W 90 KT 105 MPH 36H 13/1800Z 19.0N 119.8W 85 KT 100 MPH 48H 14/0600Z 19.2N 120.1W 80 KT 90 MPH 72H 15/0600Z 19.2N 122.2W 70 KT 80 MPH 96H 16/0600Z 18.9N 126.5W 65 KT 75 MPH 120H 17/0600Z 19.0N 131.5W 60 KT 70 MPH $$ Forecaster Cangialosi

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Tropical Storm ORLENE Forecast Discussion Number 5

2016-09-12 04:48:37| National Hurricane Center (East Pacific)

Issued at 800 PM PDT SUN SEP 11 2016 000 WTPZ41 KNHC 120248 TCDEP1 TROPICAL STORM ORLENE DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162016 800 PM PDT SUN SEP 11 2016 Visible, infrared, and microwave satellite imagery indicate that the cyclone has continued to become more organized, with a well-defined low- to mid-level eye noted in a 2336Z SSMI/S overpass. Orlene now has a large, circular CDO along with a symmetrical and expanding upper-level outflow pattern. Dvorak intensity estimates from TAFB and SAB are a consensus T3.5/55 kt while the objective UW-CIMSS ADT is 60-65 kt. Given the rather large average eye diameter of about 35 nmi, the initial intensity is set below the ADT values and follows the subjective estimate of 55 kt. The initial motion is 305/08 kt based heavily on microwave eye position estimates. Although there is some divergence in the models, they are good agreement overall on Orlene gradually slowing down and moving north-northwestward and northward into a break in the subtropical ridge during the next 48 hours. After that, the break in the ridge along 120W longitude is forecast to fill back in as a shortwave trough lifts out quickly to the northeast. The re-strengthening ridge to the north of Orlene is then expected to accelerate the cyclone on a westward track on days 3-5. The new NHC forecast track is essentially just an update and extension of the previous advisory track, and lies close to a consensus of the GFS-ECMWF model solutions. Orlene is expected to remain in a very low-shear environment for the next 72 hours, which typically favors rapid intensification. However, the cyclone is also expected to remain embedded within a fairly dry mid-level environment with humidity values of 50-55 percent. Given that Orlene has already developed a solid eyewall structure, little if any dry air intrusions should be able to penetrate into the eye in the short term. Based on the favorable low-shear and already impressive outflow pattern, a period of rapid intensification is forecast to occur for the next 24 hours, followed by a leveling off in the intensity due to cooler waters and possible cold upwelling occurring beneath the cyclone. By 48 hours and beyond, gradual weakening is expected due to Orlene moving into a considerably drier and more stable environment characterized by mid-level humidities in the 20- to 30-percent range. The intensity forecast remains near the upper end of the guidance envelope close to the LGEM and Florida State Superensemble models, and is just a little higher than the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 16.6N 118.3W 55 KT 65 MPH 12H 12/1200Z 17.3N 119.1W 70 KT 80 MPH 24H 13/0000Z 18.0N 119.7W 85 KT 100 MPH 36H 13/1200Z 18.6N 119.8W 85 KT 100 MPH 48H 14/0000Z 19.0N 120.0W 80 KT 90 MPH 72H 15/0000Z 19.2N 121.7W 70 KT 80 MPH 96H 16/0000Z 18.9N 125.7W 65 KT 75 MPH 120H 17/0000Z 18.9N 130.8W 60 KT 70 MPH $$ Forecaster Stewart

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Tropical Storm ORLENE Forecast Discussion Number 4

2016-09-11 22:33:33| National Hurricane Center (East Pacific)

Issued at 200 PM PDT SUN SEP 11 2016 000 WTPZ41 KNHC 112033 TCDEP1 TROPICAL STORM ORLENE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162016 200 PM PDT SUN SEP 11 2016 Visible, infrared, and microwave satellite images indicate that Orlene continues to become more organized. The cyclone has well-defined curved bands, and a recent SSMIS image showed that it has a mid-level eye feature. Dvorak estimates from TAFB and SAB are now T3.0/45 kt while the objective UW-CIMSS ADT is up to T3.5/55 kt. However, ASCAT data only showed maximum winds of 35-40 kt. Given this wide range, the initial intensity is raised to 45 kt for this advisory. Satellite data indicate that Orlene's center is a little bit northeast of the previous estimates, and the initial motion is now 310/12 kt. There are no changes to the forecast track reasoning. Orlene should turn northwestward and then northward and slow down drastically during the next 48 hours when it becomes positioned to the west of the subtropical ridge axis, and south of an amplifying trough over California. After 48 hours, the ridge will gradually restrengthen to the north of Orlene, forcing it toward the west with an increase in forward speed through the end of the forecast period. The official track forecast has been shifted a little northeast of the previous forecast to account for the repositioning of Orlene's center, but otherwise it still closely follows the TVCX multi-model consensus. Given Orlene's improved structure, as well as favorable sea surface temperatures and low shear, rapid intensification still looks like a possibility. The SHIPS guidance continues to indicate a 1-in-3 chance of a 30-kt increase during the next 24 hours, and the raw guidance itself brings Orlene to a hurricane in about 24 hours. The NHC intensity forecast continues to show a peak intensity close to the SHIPS and Florida State Superensemble in about 36 hours, which is at the top end of the guidance envelope. After 36 hours, Orlene's slow motion over sea surface temperatures between 26-27C is likely to lead to upwelling of colder water, and the cyclone is expected to gradually weaken through the end of the forecast period. This new forecast is essentially unchanged from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 16.3N 117.7W 45 KT 50 MPH 12H 12/0600Z 17.0N 118.8W 55 KT 65 MPH 24H 12/1800Z 17.9N 119.6W 70 KT 80 MPH 36H 13/0600Z 18.6N 119.9W 80 KT 90 MPH 48H 13/1800Z 19.1N 119.9W 75 KT 85 MPH 72H 14/1800Z 19.5N 120.9W 70 KT 80 MPH 96H 15/1800Z 19.0N 124.0W 65 KT 75 MPH 120H 16/1800Z 19.0N 129.5W 60 KT 70 MPH $$ Forecaster Berg

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Tropical Storm ORLENE Forecast Discussion Number 3

2016-09-11 16:41:02| National Hurricane Center (East Pacific)

Issued at 800 AM PDT SUN SEP 11 2016 000 WTPZ41 KNHC 111440 TCDEP1 TROPICAL STORM ORLENE DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162016 800 AM PDT SUN SEP 11 2016 A central dense overcast has become established over Orlene's center, with very cold temperatures of -86C at cloud top level. There is little to no deep-layer shear, and the cyclone has very good upper-level outflow, especially to the north and west. Because the Dvorak rules don't yet allow the use of an embedded center pattern, estimates from TAFB and SAB are still at T2.5. However, the objective UW-CIMSS ADT is higher, and given the more consolidated structure compared to six hours ago, the initial intensity is raised to 40 kt. Orlene is moving northwestward, or 305/12 kt, to the southwest of a mid-tropospheric high located over northern Mexico. Over the next few days, Orlene is expected to become trapped in an environment of weak steering to the west of the subtropical ridge axis and south of an amplifying trough over California. This should cause the cyclone to turn north-northwestward and slow to a crawl by days 2 and 3. After that time, a re-establishment of the ridge should force an acceleration toward the west on days 4 and 5. There is not much spread among the track models during the entire forecast period. Except for a slight northeastward shift at 36 and 48 hours, the updated NHC forecast is nearly identical to the previous one and lies closest to the TVCX multi-model consensus and Florida State Superensemble. Low shear and warm sea surface temperatures are expected to support additional strengthening, and there are signs that rapid intensification could occur. There is a 1-in-3 chance of a 30-kt intensity increase during the next 24 hours, and several intensity models bring Orlene near or to hurricane strength in about 24 hours. Given the seemingly favorable environment, the NHC intensity forecast is closest to the most aggressive intensity models like the Florida State Superensemble, and it is higher than the previous forecast during the first 48 hours. Orlene's intensity could be limited once it slows down in 48-72 hours due to upwelling of colder water, and thus the official forecast shows gradual weakening after day 2. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 15.4N 116.8W 40 KT 45 MPH 12H 12/0000Z 16.2N 118.2W 50 KT 60 MPH 24H 12/1200Z 17.1N 119.4W 65 KT 75 MPH 36H 13/0000Z 17.9N 120.0W 80 KT 90 MPH 48H 13/1200Z 18.5N 120.2W 80 KT 90 MPH 72H 14/1200Z 19.1N 120.9W 75 KT 85 MPH 96H 15/1200Z 19.0N 123.5W 70 KT 80 MPH 120H 16/1200Z 18.5N 128.5W 65 KT 75 MPH $$ Forecaster Berg

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