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Tropical Storm Hilary Forecast Discussion Number 38
2017-07-30 22:40:41| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Sun Jul 30 2017 000 WTPZ44 KNHC 302040 TCDEP4 Tropical Storm Hilary Discussion Number 38 NWS National Hurricane Center Miami FL EP092017 200 PM PDT Sun Jul 30 2017 Convection continues to gradually decline with cloud tops of -20C to -25C now located near the low-level center and in the northern semicircle. Although the convective pattern has taken on more of a stratiform appearance, an 1840Z ASCAT-B overpass indicated that Hilary is still a tropical storm based on several 35- to 37-kt wind vectors located in the northeastern quadrant. Therefore, the initial intensity remains 35 kt for this advisory. Continued steady weakening is expected as Hilary moves over SSTs near 21C and ingests stable stratocumulus clouds throughout the forecast period, with the cyclone likely degenerating into a remnant low pressure system tonight or early Monday. The initial motion estimate is 300/12 kt. There is no significant change to the previous forecast track or rationale. The latest NHC model guidance is in excellent agreement on Hilary moving west-northwestward for the next 24 hours or so, followed by the shallow cyclone turning a little more westward under the influence of brisk easterly tradewinds until dissipation occurs by 72 h. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 25.0N 127.2W 35 KT 40 MPH 12H 31/0600Z 25.9N 129.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 31/1800Z 26.7N 131.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 01/0600Z 27.2N 132.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 01/1800Z 27.5N 134.3W 15 KT 15 MPH...POST-TROP/REMNT LOW 72H 02/1800Z...DISSIPATED $$ Forecaster Stewart
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Tropical Storm IRWIN Forecast Discussion Number 34
2017-07-30 22:32:06| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Sun Jul 30 2017 000 WTPZ45 KNHC 302031 TCDEP5 Tropical Storm Irwin Discussion Number 34 NWS National Hurricane Center Miami FL EP102017 200 PM PDT Sun Jul 30 2017 Although the mid-level eye feature is no longer evident in satellite images, the compact circulation of Irwin is still fairly well organized. The convective pattern consists of a central dense overcast with fragmented curved bands mostly to the south of the center. The Dvorak CI-numbers from TAFB and SAB remain 3.5/55 kt, so the initial intensity is held at that value. Irwin has now crossed the 26 deg C isotherm, and it will be headed for even cooler waters during the next few days. In addition, a large area of stratocumulus clouds are wrapping into the western and southern portions of the circulation, indicative of stable air beginning to affect the system. These unfavorable environmental conditions should lead to steady weakening and ultimately cause Irwin to degenerate into a remnant low in about 36 hours, or possibly sooner. The remnant low is now expected to dissipate by day 4, following the global model guidance. The NHC intensity forecast is largely an update of the previous one and in line with the bulk of the guidance. Irwin is moving north-northwestward, or 335 degrees, at 8 kt embedded in the flow in the wake of Hilary. This motion with an increase in forward speed is expected during the next day or two. Once Irwin becomes a remnant low, the shallow system is expected to turn a little to the left and slow down when it becomes steered by the low-level flow. The NHC track forecast is similar to the previous one, and it lies close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 18.5N 125.6W 55 KT 65 MPH 12H 31/0600Z 20.3N 126.5W 50 KT 60 MPH 24H 31/1800Z 22.6N 127.7W 40 KT 45 MPH 36H 01/0600Z 24.7N 129.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 01/1800Z 26.4N 130.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 02/1800Z 28.1N 132.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 03/1800Z...DISSIPATED $$ Forecaster Cangialosi
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Tropical Storm Irwin Forecast Discussion Number 33
2017-07-30 16:36:34| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Sun Jul 30 2017 000 WTPZ45 KNHC 301436 TCDEP5 Tropical Storm Irwin Discussion Number 33 NWS National Hurricane Center Miami FL EP102017 800 AM PDT Sun Jul 30 2017 Even though Irwin is crossing the 26 deg C isotherm, it does not appear to be weakening yet. In fact, recent microwave data indicate the tropical storm has a mid-level eye, which has occasionally appeared in geostationary satellite images. The system is still producing a fair amount of deep convection, especially to the south of the center. The latest Dvorak CI-numbers from TAFB and SAB are 3.5/55 kt and accordingly, the initial intensity is set a bit higher to 55 kt. This wind speed estimate is also in agreement with ASCAT data from several hours ago that showed maximum winds near 50 kt. Despite the recent increase in intensity, Irwin is expected to begin weakening soon as it moves over even cooler waters and into a drier and more stable air mass. The storm is likely to become a remnant low in 36 to 48 hours when it will be over SSTs near 22 deg C. Most of the global models show the remnant low dissipating in 4 to 5 days. The NHC intensity forecast follows the trend of the guidance, and it is largely unchanged from the previous prediction. Irwin is moving north-northwestward, or 345 degrees, at 8 kt. The system is embedded in south-southeasterly flow in the wake of Hilary, and it is expected to remain in this steering flow for another day or two. Once Irwin becomes a remnant low, the shallow system is expected to turn a little to the left and slow down as it becomes steered by the low-level flow. The NHC track forecast is adjusted a little to the north and east of the previous one, to come into better agreement with the latest consensus models. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 17.9N 125.4W 55 KT 65 MPH 12H 31/0000Z 19.4N 126.1W 50 KT 60 MPH 24H 31/1200Z 21.7N 127.3W 40 KT 45 MPH 36H 01/0000Z 23.9N 128.6W 35 KT 40 MPH 48H 01/1200Z 25.7N 130.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 02/1200Z 27.9N 132.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 03/1200Z 29.0N 133.2W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 04/1200Z...DISSIPATED $$ Forecaster Cangialosi
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Tropical Storm Hilary Forecast Discussion Number 37
2017-07-30 16:34:03| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Sun Jul 30 2017 000 WTPZ44 KNHC 301433 TCDEP4 Tropical Storm Hilary Discussion Number 37 NWS National Hurricane Center Miami FL EP092017 800 AM PDT Sun Jul 30 2017 Convection has continued to rapidly wane with only a small band of modest thunderstorm activity with tops to -30C restricted to the southeastern quadrant. The initial intensity has been lowered to 35 kt based on a blend of available intensity estimates from TAFB, SAB, and UW-CIMSS ADT and SATCON. This rapid weakening trend is forecast to continue since Hilary is now moving over sub-22 C SSTs and into an extensive field of stable, cold-air stratocumulus clouds. These unfavorable thermodynamic conditions should cause Hilary to degenerate into a remnant low pressure system tonight, if not sooner. The initial motion estimate is 300/11 kt. As Hilary continues to lose its deep vertical circulation, the shallow cyclone should maintain a general west-northwestward motion along the southern periphery of a deep-layer ridge until dissipation occurs in 72 h. The NHC track forecast remains along the southern portion of the tightly clustered guidance and is close to the previous advisory track. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 23.9N 125.7W 35 KT 40 MPH 12H 31/0000Z 24.9N 127.7W 30 KT 35 MPH 24H 31/1200Z 25.8N 129.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 01/0000Z 26.3N 131.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 01/1200Z 26.7N 133.2W 15 KT 15 MPH...POST-TROP/REMNT LOW 72H 02/1200Z...DISSIPATED $$ Forecaster Stewart
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Tropical Storm Irwin Forecast Discussion Number 32
2017-07-30 10:53:03| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Sun Jul 30 2017 000 WTPZ45 KNHC 300852 TCDEP5 Tropical Storm Irwin Discussion Number 32 NWS National Hurricane Center Miami FL EP102017 200 AM PDT Sun Jul 30 2017 Infrared and earlier microwave satellite pictures show that Irwin remains fairly well organized. An 0308 UTC AMSU microwave overpass revealed a curved band over the southeastern portion of the circulation and a mid-level eye-like feature. Recent ASCAT data suggest that Irwin is slightly stronger than earlier estimates, so the initial wind speed has been set at 50 kt for this advisory. Irwin is forecast to move north of the 26 deg C isotherm later this morning, and over even colder waters within the next 36 to 48 hours. As a result, Irwin is expected to gradually weaken over the next few days, and the cyclone is forecast to become a remnant low late Monday. The new NHC wind speed forecast is identical to the previous advisory and close to the various consensus aids. Irwin has begun its much anticipated northward acceleration, with recent satellite fixes indicating a motion of 350/8 kt. The tropical storm is forecast to turn north-northwestward today and continue to accelerate in south-southeasterly low- to mid-level flow in the wake of Hilary. In 36 to 48 hours, Irwin is forecast to turn northwestward and slow down when it approaches Hilary's remnant low. The dynamical model guidance is tightly clustered through 48 h, with some spread later in the period. The NHC track is similar to the previous advisory and is near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 17.1N 125.0W 50 KT 60 MPH 12H 30/1800Z 18.7N 125.5W 45 KT 50 MPH 24H 31/0600Z 20.9N 126.7W 40 KT 45 MPH 36H 31/1800Z 23.2N 128.1W 35 KT 40 MPH 48H 01/0600Z 25.2N 129.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 02/0600Z 27.5N 132.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 03/0600Z 28.5N 133.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 04/0600Z...DISSIPATED $$ Forecaster Brown
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