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Tropical Depression Fourteen Forecast Discussion Number 3

2018-10-07 10:52:09| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Sun Oct 07 2018 000 WTNT44 KNHC 070851 TCDAT4 Tropical Depression Fourteen Discussion Number 3 NWS National Hurricane Center Miami FL AL142018 400 AM CDT Sun Oct 07 2018 Radar data from Belize and infrared satellite imagery indicate that the low pressure system centered just off the coast of the Yucatan Peninsula has continued to become better organized, with deep convection consolidating just to the northeast of the low-level center. Dvorak estimates have increased to T2.0 from TAFB and T1.5 from SAB, indicating that the convective pattern has become sufficiently organized for the low to now be declared a tropical depression. The maximum winds are estimated to be 30 kt based on earlier ASCAT data. The Belize radar data was extremely helpful in locating the depression's center, and the system's 12-hour average motion is north-northwestward, or 340 degrees, at a very slow 3 kt. The depression is expected to move generally northward during the next 3 days, gradually gaining speed as it enters the southerly flow between high pressure over the western Atlantic and an advancing deep-layer trough over the western half of the United States. After day 3, the trough is expected to cause the cyclone to turn northeastward and accelerate further across the southeastern United States. While the track models agree on the general scenario, there are some speed differences, most notably with the ECMWF model being slower than the other guidance. Also, the ECMWF and GFS models are located along the western edge of the guidance envelope. In light of these facts, the new NHC prediction is just a little slower than the previous one, and it lies to the west of the TVCN multi-model consensus and the HCCA model during the first 3 days of the forecast. The depression is still being hampered by 20-30 kt of westerly shear, however it is also located in an environment of upper-level diffluence to the southeast of a stationary trough over the Gulf of Mexico. The shear in the immediate vicinity of the cyclone is forecast to gradually abate during the next 2-3 days while the diffluent upper-air pattern continues, and along with sufficiently warm waters of 28-30 degrees Celsius, all indications are that the depression will gradually strengthen while it moves northward over the Gulf of Mexico. In fact, nearly every piece of intensity guidance brings the cyclone to hurricane strength before it reaches land, including the GFS, ECMWF, and UKMET global models, which all show significant deepening of the central pressure. The updated NHC intensity forecast generally lies between the ICON intensity consensus and the HCCA model for the entire forecast period, and it now explicitly shows the cyclone reaching hurricane strength by 72 hours. Key Messages for Tropical Depression Fourteen: 1. The depression is producing heavy rainfall and flash flooding over portions of Central America, and these rains will spread over western Cuba and the northeastern Yucatan Peninsula of Mexico during the next couple of days. 2. The depression is forecast to become a tropical storm later today, and tropical storm conditions are expected by tonight over portions of western Cuba and the northeastern Yucatan Peninsula, where tropical storm warnings are in effect. 3. Storm surge, rainfall, and wind impacts are possible over portions of the northern Gulf Coast by mid-week, although it is too soon to specify the exact location and magnitude of these impacts. Residents in these areas should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 18.6N 86.9W 30 KT 35 MPH 12H 07/1800Z 19.4N 86.7W 35 KT 40 MPH 24H 08/0600Z 20.8N 86.4W 45 KT 50 MPH 36H 08/1800Z 22.3N 86.6W 50 KT 60 MPH 48H 09/0600Z 23.9N 87.1W 55 KT 65 MPH 72H 10/0600Z 27.6N 87.3W 65 KT 75 MPH 96H 11/0600Z 32.0N 84.0W 45 KT 50 MPH...INLAND 120H 12/0600Z 37.0N 76.0W 45 KT 50 MPH...NEAR THE VA COAST $$ Forecaster Berg

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Tropical Storm Leslie Forecast Discussion Number 44

2018-10-07 10:49:07| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sun Oct 07 2018 000 WTNT43 KNHC 070848 TCDAT3 Tropical Storm Leslie Discussion Number 44 NWS National Hurricane Center Miami FL AL132018 500 AM AST Sun Oct 07 2018 Leslie has not changed much overnight. The storm has several curved bands to the east and north of the center, but a limited amount of deep convection in the southwestern quadrant. The initial intensity is held at 50 kt based on the steady state appearance since the previous ASCAT pass. This estimate is also in fair agreement with the latest Dvorak estimates from TAFB and SAB. Leslie will likely fluctuate in strength during the next several days, but it should remain a tropical storm through the forecast period. Although some weakening is possible during the next day or so due to cool 23 to 24 deg C waters, slight re-strengthening is likely after that time when the system moves back over warmer waters and remains in relatively low wind shear conditions. There could be some increase in shear by the end of the forecast period, however, which could result in slight weakening again. The models are in fairly good agreement, and the NHC intensity forecast is close to the IVCN and HCCA consensus models. Leslie is moving eastward at 10 kt within the mid-latitude westerly flow on the south side of a broad mid- to upper-level trough. This trough is expected to amplify some, which should cause the storm to move east-southeastward at a faster pace during the next few days. A slight turn back to the east or east-northeast with a decrease in forward speed is likely by the end of the forecast period when the trough weakens. There is a significant amount of spread in the models associated with differences on how fast they expect Leslie to move. In fact, the GFS and ECMWF models are more than 1000 n mi apart by day 5. The NHC track forecast is a little slower than the previous one at the end of the period to come in better agreement with the latest consensus aids. Given the model spread, the confidence in the long-range track forecast is low at this time. Large swells generated by Leslie are expected to continue through tonight across the northeastern coast of the United States, Bermuda, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 37.2N 52.0W 50 KT 60 MPH 12H 07/1800Z 36.6N 50.3W 45 KT 50 MPH 24H 08/0600Z 36.1N 48.0W 45 KT 50 MPH 36H 08/1800Z 35.1N 45.1W 50 KT 60 MPH 48H 09/0600Z 33.7N 42.2W 55 KT 65 MPH 72H 10/0600Z 30.1N 36.0W 55 KT 65 MPH 96H 11/0600Z 28.6N 32.0W 55 KT 65 MPH 120H 12/0600Z 29.5N 27.2W 50 KT 60 MPH $$ Forecaster Cangialosi

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Hurricane Sergio Forecast Discussion Number 31

2018-10-07 05:01:19| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Sat Oct 06 2018 000 WTPZ41 KNHC 070301 TCDEP1 Hurricane Sergio Discussion Number 31 NWS National Hurricane Center Miami FL EP212018 800 PM PDT Sat Oct 06 2018 Little overall change has been noted in Sergio's satellite presentation the past several hours other than cloud tops have warmed slightly. The 30-nmi-wide eye remains quite distinct and outflow is still very impressive in all quadrants. However, he warming tops have resulted in slightly lower satellite intensity estimates from all agencies, so the initial intensity has been lowered to 105 kt for this advisory. Sergio is lumbering along toward the west, or 270/06 kt. There is no significant change to the previous forecast track or reasoning. Sergio should continue to move slowly westward around the southwestern periphery of a weak deep-layer ridge for the next day or so. By early next week, a strong trough is forecast to dig southward off the coasts of California and Baja California, which will erode the ridge and cause Sergio to make a sharp northeastward turn and accelerate throughout the forecast period. The latest NHC track guidance remains in good agreement on this developing steering flow pattern, and there is very little cross-track spread in the models. The speed differences noted in the previous discussion have decreased on this forecast cycle, so only minor tweaks had to be made to the previous advisory track. The new forecast track lies close the previous one and near a blend of the various consensus track models. Ocean temperatures beneath the cyclone are forecast to decrease over the next few days due to cold upwelling beneath the hurricane, so gradual weakening is expected for the next 3 days. After that, more rapid weakening is forecast due to increasing southwesterly vertical wind shear ahead of a a deep-layer trough. The NHC intensity forecast is very similar to the previous advisory and the IVCN consensus model. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 14.5N 125.4W 105 KT 120 MPH 12H 07/1200Z 14.5N 126.4W 100 KT 115 MPH 24H 08/0000Z 14.8N 127.2W 95 KT 110 MPH 36H 08/1200Z 15.4N 127.6W 90 KT 105 MPH 48H 09/0000Z 16.1N 127.4W 85 KT 100 MPH 72H 10/0000Z 18.0N 124.9W 75 KT 85 MPH 96H 11/0000Z 20.9N 120.6W 60 KT 70 MPH 120H 12/0000Z 25.6N 115.1W 45 KT 50 MPH $$ Forecaster Stewart

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Tropical Storm Leslie Forecast Discussion Number 43

2018-10-07 04:49:35| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sat Oct 06 2018 000 WTNT43 KNHC 070249 TCDAT3 Tropical Storm Leslie Discussion Number 43 NWS National Hurricane Center Miami FL AL132018 1100 PM AST Sat Oct 06 2018 Leslie's convective organization has changed little since the previous advisory, with a small burst of deep convection having developed just southeast of the center. The intensity remains at 50 kt based on an average of current intensity estimates from TAFB and SAB, which is supported by a partial ASCAT pass that showed several 45-kt surface wind vectors well east of the missed low-level center. The initial motion estimate is easterly or 095/11 kt. Leslie is forecast to remain embedded in weak mid-latitude west-northwesterly flow for the next few days, which should keep the cyclone moving toward the east-southeast over warmer water. By 72 h and beyond, a stronger shortwave trough is forecast to dig to the west of Leslie, lifting the cyclone out toward the east and northeast. The new NHC forecast track is similar to, but a slower than, the previous advisory track, but not as slow as the consensus models. Leslie is expected to weaken slightly during the next 36 h as the cyclone entrains some drier air. After that time, however, Leslie is expected to move over warmer waters with SSTs reaching more than 25 deg C by 48 h and beyond while the shear is forecast to remain low. As a result, some modest re-strengthening is forecast on days 2-5. The official intensity forecast closely follows the IVCN intensity consensus model. Large swells generated by Leslie are expected to continue during the next few days across the northeastern coast of the United States, Bermuda, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 37.3N 52.9W 50 KT 60 MPH 12H 07/1200Z 36.8N 51.2W 45 KT 50 MPH 24H 08/0000Z 36.2N 48.8W 45 KT 50 MPH 36H 08/1200Z 35.4N 46.4W 45 KT 50 MPH 48H 09/0000Z 34.2N 43.7W 50 KT 60 MPH 72H 10/0000Z 30.9N 38.5W 55 KT 65 MPH 96H 11/0000Z 28.7N 33.9W 55 KT 65 MPH 120H 12/0000Z 29.5N 28.5W 55 KT 65 MPH $$ Forecaster Stewart

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Potential Tropical Cyclone Fourteen Forecast Discussion Number 2

2018-10-07 04:36:05| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Sat Oct 06 2018 000 WTNT44 KNHC 070235 TCDAT4 Potential Tropical Cyclone Fourteen Discussion Number 2 NWS National Hurricane Center Miami FL AL142018 1000 PM CDT Sat Oct 06 2018 The cloud pattern has improved in organization and surface pressures are gradually falling, but there is no evidence that the system is a tropical cyclone at this time. All indications are, however, that a tropical depression will likely form at any time soon. Strong wind shear is expected to affect the disturbance, and the SHIPS model only show a modest strengthening. This is in contrast to some global models and the HWRF, which are more aggressive in developing this system. Since the environment is marginally favorable, the NHC forecast only gradually strengthens the system at the rate of the intensity consensus IVCN. However, the forecast is highly uncertain given the solution of the global models. Since the system does not have a well-defined center, the initial motion is also uncertain. The best estimate is toward the north or 360 degrees at 6 kt. Over the next 2 or 3 days, the cyclone will be embedded within the deep southerly flow between a strong subtropical ridge over the western Atlantic and a sharp mid-latitude trough advancing eastward over the United States. This flow pattern will force the system to move northward at 5 to 10 kt across the eastern Gulf of Mexico for the next 2 to 3 days. By day 4, the system should have moved inland and be weakening. It should then race northeastward farther inland across the eastern U.S. The track guidance envelope is remarkably quite tight. This increases the confidence in the track forecast primarily after the cyclone forms. Key Messages for Potential Tropical Cyclone Fourteen: 1. This system is producing heavy rainfall and flash flooding over portions of Central America, and these rains will spread over western Cuba and the northeastern Yucatan Peninsula of Mexico during the next couple of days. 2. The system is forecast to become a tropical storm by late Sunday, and tropical storm conditions are expected over portions of western Cuba, where a Tropical Storm Warning is in effect. 3. The system could bring storm surge, rainfall, and wind impacts to portions of the northern Gulf Coast by mid-week, although it is too soon to specify the exact location and magnitude of these impacts. Residents in these areas should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 18.8N 86.6W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 07/1200Z 19.5N 86.5W 30 KT 35 MPH...TROPICAL CYCLONE 24H 08/0000Z 21.0N 86.2W 35 KT 40 MPH 36H 08/1200Z 22.3N 86.1W 40 KT 45 MPH 48H 09/0000Z 23.8N 86.3W 45 KT 50 MPH 72H 10/0000Z 27.4N 87.2W 55 KT 65 MPH 96H 11/0000Z 32.0N 85.0W 30 KT 35 MPH...INLAND 120H 12/0000Z 38.5N 77.5W 30 KT 35 MPH...INLAND $$ Forecaster Avila

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