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Tropical Storm Harvey Forecast Discussion Number 16
2017-08-24 16:55:06| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Thu Aug 24 2017 000 WTNT44 KNHC 241455 TCDAT4 Tropical Storm Harvey Discussion Number 16 NWS National Hurricane Center Miami FL AL092017 1000 AM CDT Thu Aug 24 2017 Data from an Air Force Hurricane Hunter aircraft indicate that Harvey is quickly strengthening, and the cyclone's structure has improved markedly with the plane reporting a closed 15-20 n mi wide eye. The flight-level and SFMR winds support an intensity of 55 kt, but one of the more notable measurements is the central pressure, which has fallen to 982 mb. With a pressure this low, it is likely that the winds will respond and increase further, and Harvey probably isn't too far from becoming a hurricane. With Harvey now strengthening at a faster rate than indicated in previous advisories, the intensity forecast has become quite concerning. Water vapor images indicate that the cyclone's outflow is expanding--indicative of low shear--and Harvey will be moving over a warm eddy of high oceanic heat content in the western Gulf of Mexico in about 24 hours. As a result of these conditions, several intensity models, including the ICON intensity consensus, are now explicit showing Harvey reaching major hurricane intensity. What's more astounding is that some of the SHIPS Rapid Intensification indices are incredibly high. As an example, the guidance is indicating a 70 percent chance of Harvey's winds increasing by 45 kt over the next 36 hours. Based on this guidance, the NHC official intensity forecast now calls for Harvey to reach major hurricane strength by 36 hours, before it reaches the middle Texas coast. Aircraft fixes indicate that Harvey has turned toward the north- northwest, and the initial motion estimate is 340/9 kt. A mid- level high centered near Florida and the eastern Gulf of Mexico should force Harvey toward the northwest later today, with that trajectory continuing for the next couple of days. By 48 hours, the cyclone appears to get sandwiched between the same mid-level high over the Gulf of Mexico and a larger high over the Intermountain West, which will cause Harvey to slow down considerably during its approach toward the Texas coast and then potentially stall just inland on days 3 through 5. Mainly based on an adjustment of the initial position, the NHC forecast track has been nudged northeastward on this cycle, but it still lies relatively close to the TVCN multi-model consensus and the HFIP Corrected Consensus Approach (HCCA). It is critical that users not focus on the exact forecast track of Harvey, since cycle-to-cycle adjustment are likely. All locations within the hurricane and storm surge warning areas should be preparing for the possibility of major hurricane-force winds and life-threatening storm surge. Key Messages: 1. Harvey has intensified quickly this morning, and is now forecast to be a major hurricane at landfall, bringing life-threatening storm surge, rainfall, and wind hazards to portions of the Texas coast. Preparations to protect life and property should be completed by tonight, as tropical-storm-force winds will first arrive in the hurricane and storm surge warning areas on Friday. 2. A Storm Surge Warning is in effect for much of the Texas coast. Life-threatening storm surge flooding could reach heights of 6 to 10 feet above ground level at the coast between the north entrance of the Padre Island National Seashore and Sargent. For a depiction of areas at risk, see the Storm Surge Watch/Warning Graphic at hurricanes.gov. 3. Life-threatening flooding is expected across much of the Texas coast from heavy rainfall of 12 to 20 inches, with isolated amounts as high as 30 inches, from Friday through early next week. Please refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. 4. The Potential Storm Surge Flooding Map is available on the NHC website. This product depicts a reasonable worst-case scenario - the amount of inundation that has a 10 percent chance of being exceeded at each individual location. This map best represents the flooding potential in those locations within the watch and warning areas. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 24.0N 93.3W 55 KT 65 MPH 12H 25/0000Z 24.9N 94.2W 70 KT 80 MPH 24H 25/1200Z 26.0N 95.3W 90 KT 105 MPH 36H 26/0000Z 27.3N 96.3W 100 KT 115 MPH 48H 26/1200Z 28.3N 97.0W 95 KT 110 MPH...INLAND 72H 27/1200Z 29.0N 97.7W 40 KT 45 MPH...INLAND 96H 28/1200Z 28.5N 97.5W 35 KT 40 MPH...INLAND 120H 29/1200Z 28.5N 96.5W 30 KT 35 MPH...INLAND $$ Forecaster Berg
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Tropical Storm Harvey Forecast Discussion Number 15
2017-08-24 10:56:34| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Thu Aug 24 2017 000 WTNT44 KNHC 240856 TCDAT4 Tropical Storm Harvey Discussion Number 15 NWS National Hurricane Center Miami FL AL092017 400 AM CDT Thu Aug 24 2017 NOAA and Air Force Hurricane Hunter planes have been sampling Harvey during the past few hours. Both aircraft indicate that Harvey is becoming better organized and the central pressure is falling. An average of the flight-level winds and the SFMR yield an initial intensity of 40 kt. There are some unconfirmed reports of stronger winds at flight-level to the northeast of the center, but I am waiting for the plane to go back to that area for confirmation. It appears that the environment has finally become favorable and all of the guidance calls for intensification. In fact, the Rapid Intensification Index is up to 45 percent. The current NHC forecast is a little lower than the model consensus to maintain continuity from the previous advisory. If the current intensity trend continues, the winds will have to be adjusted upward in the next advisory. The initial motion is toward the north or 360 degrees at 9 kt. However, this is a combination of motion and reformation under the convection. Harvey is already on the western edge of the subtropical ridge extending from the Atlantic westward across the Gulf of Mexico. This pattern will steer the cyclone on a general northwest to north-northwest track for the next 2 to 3 days. Once Harvey makes landfall in Texas, most of the global models predict that the steering currents will collapse and Harvey will begin to meander over Texas and perhaps will move back into the northwestern Gulf of Mexico. Key Messages: 1. Harvey is likely to bring multiple hazards, including heavy rainfall, storm surge, and possible hurricane conditions to portions of the Texas coast beginning on Friday. 2. Heavy rainfall is likely to spread across portions of eastern Texas, Louisiana, and the lower Mississippi Valley from Friday through early next week and could cause life-threatening flooding. Please refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. 3. A Storm Surge Warning is now effect from Port Mansfield to San Luis Pass, Texas, indicating the possibility of life-threatening inundation from rising water moving inland from the coast during the next 36 hours. For a depiction of areas at risk, see the Storm Surge Watch/Warning Graphic at hurricanes.gov. 4. The Potential Storm Surge Flooding Map is available on the NHC website. This product depicts a reasonable worst-case scenario - the amount of inundation that has a 10 percent chance of being exceeded at each individual location. Because the Flooding Map is based on inputs that extend out only to about 72 hours, it best represents the flooding potential in those locations within the watch area. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 23.2N 92.8W 40 KT 45 MPH 12H 24/1800Z 24.0N 93.6W 50 KT 60 MPH 24H 25/0600Z 25.1N 94.8W 60 KT 70 MPH 36H 25/1800Z 26.3N 95.8W 70 KT 80 MPH 48H 26/0600Z 27.5N 97.0W 75 KT 85 MPH 72H 27/0600Z 28.5N 97.8W 40 KT 45 MPH...INLAND 96H 28/0600Z 28.5N 97.8W 35 KT 40 MPH...INLAND 120H 29/0600Z 27.6N 97.0W 35 KT 40 MPH...INLAND $$ Forecaster Avila
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Tropical Depression Harvey Forecast Discussion Number 14
2017-08-24 04:38:36| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Wed Aug 23 2017 000 WTNT44 KNHC 240238 TCDAT4 Tropical Depression Harvey Discussion Number 14 NWS National Hurricane Center Miami FL AL092017 1000 PM CDT Wed Aug 23 2017 Reports from an Air Force Reserve Hurricane Hunter aircraft suggest that Harvey's structure has consolidated a little bit, with the pressure falling to 1002 mb and the radius of maximum winds shrinking to 60 n mi. However, there have been no reliable reports of winds indicating that the cyclone has reached tropical-storm strength, and the convective cloud pattern remains ragged. Based on these data, the initial intensity is held at 30 kt. Perhaps the most significant finding of the aircraft is that the center was to the east of the previous advisory position. The initial motion is a rather uncertain 325/2. A weak mid-level ridge to the northeast of Harvey should cause the cyclone to move on a northwestward or north-northwestward track through 48-72 h, and this motion should bring the center inland over southern Texas. Later, steering currents weaken as a ridge builds over the southwestern United States and a trough drops down from the Plains. As a result, Harvey should decelerate while making landfall and move very slowly just inland of the coast. There is a major spread amongst the large-scale models from 72-120 h, with the UKMET forecasting a slow northward motion into eastern Texas, the GFS a southwestward motion over Texas, and the ECMWF a cyclonic loop that moves the system back over the Gulf of Mexico. Given the uncertainty, the new forecast track shows a slow motion over southern Texas during that time, with a change from the small right turn of the previous forecast to a small left turn. Overall, the track lies a little to the right of the consensus models through 72 h. An upper-level low seen in water vapor imagery over the northwestern Gulf of Mexico appears to be weakening, and as this happens Harvey should end up in a low shear environment. This should allow strengthening over deep warm water in the western Gulf of Mexico. The new intensity forecast is adjusted slightly to show Harvey explicitly becoming a hurricane in 48 h, and some additional strengthening could occur between the 48 h point and landfall. After landfall, Harvey is expected to weaken. However, the forecast track keeps the system close enough to the Texas coast that this weakening is likely to be slower than normal. Since Harvey has moved slower than anticipated during the past 6-12 h, warnings are not yet required for portions of the Texas coast. Warnings are likely to be issued sometime on Thursday. Key Messages: 1. Harvey is likely to bring multiple hazards, including heavy rainfall, storm surge, and possible hurricane conditions to portions of the Texas coast beginning on Friday. 2. Heavy rainfall is likely to spread across portions of eastern Texas, Louisiana, and the lower Mississippi Valley from Friday through early next week and could cause life-threatening flooding. Please refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. 3. A Storm Surge Watch is in effect from Port Mansfield to High Island, Texas, indicating the possibility of life-threatening inundation from rising water moving inland from the coast during the next 48 hours. For a depiction of areas at risk, see the Storm Surge Watch/Warning Graphic at hurricanes.gov. 4. The Potential Storm Surge Flooding Map is available on the NHC website. This product depicts a reasonable worst-case scenario - the amount of inundation that has a 10 percent chance of being exceeded at each individual location. Because the Flooding Map is based on inputs that extend out only to about 72 hours, it best represents the flooding potential in those locations within the watch area. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 21.9N 92.6W 30 KT 35 MPH 12H 24/1200Z 22.8N 93.1W 35 KT 40 MPH 24H 25/0000Z 24.1N 94.1W 40 KT 45 MPH 36H 25/1200Z 25.4N 95.4W 50 KT 60 MPH 48H 26/0000Z 26.6N 96.3W 65 KT 75 MPH 72H 27/0000Z 28.5N 97.5W 50 KT 60 MPH...INLAND 96H 28/0000Z 28.5N 98.0W 35 KT 40 MPH...INLAND 120H 29/0000Z 28.0N 98.0W 30 KT 35 MPH...INLAND $$ Forecaster Beven
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Tropical Depression Harvey Forecast Discussion Number 13
2017-08-23 22:37:31| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Wed Aug 23 2017 000 WTNT44 KNHC 232037 TCDAT4 Tropical Depression Harvey Discussion Number 13 NWS National Hurricane Center Miami FL AL092017 400 PM CDT Wed Aug 23 2017 High-resolution visible satellite images show that the cloud pattern of Harvey is a little better organized than it was this morning, but the system lacks distinct banding features. Surface synoptic observations, ASCAT data, and Dvorak classifications from TAFB and SAB indicated that the cyclone has not strengthened, so the current intensity is held at 30 kt. The global models predict that an upper-level low over the northwest Gulf of Mexico will essentially dissipate in a day or so. Therefore, Harvey is expected to remain in a relatively low-shear environment up to the Texas coast. Moreover, ocean analyses show that a warm eddy that broke off from the Loop Current has drifted westward across the Gulf to a location near the projected path of Harvey. This would also be conducive to strengthening, so it is likely that the system will become a hurricane prior to landfall, although this is not explicitly shown in the NHC forecast for which landfall is indicated between 48 and 72 hours. Based on the scatterometer data and geostationary satellite fixes the center hasn't moved much this afternoon, although recent imagery suggests a northwestward drift at about 320/2 kt. A weak mid-level ridge to the northeast of Harvey should cause the cyclone to move on a northwestward or north-northwestward track through 48 hours. Later, steering currents weaken as a ridge builds over the southwestern United States and a trough drops down from the Plains. As a result, Harvey should decelerate while making landfall and move very slowly just inland of the coast. Some of the track guidance models, such as the HWRF, have shifted southwestward in comparison to their previous run. The official track forecast is very close to the previous one through 48 hours and is a little slower and to the west after that time. This is very close to the latest dynamical model consensus, TVCN. It should be noted that synoptic surveillance data are currently being collected by the NOAA G-IV jet aircraft and these data will be assimilated into, and hopefully improve the forecasts by, the global models. Key Messages: 1. Harvey is likely to bring multiple hazards, including heavy rainfall, storm surge, and possible hurricane conditions to portions of the Texas coast beginning on Friday. 2. Heavy rainfall is likely to spread across portions of eastern Texas, Louisiana, and the lower Mississippi Valley from Friday through early next week and could cause life-threatening flooding. Please refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. 3. A Storm Surge Watch is in effect from Port Mansfield to High Island, Texas, indicating the possibility of life-threatening inundation from rising water moving inland from the coast during the next 48 hours. For a depiction of areas at risk, see the Storm Surge Watch/Warning Graphic at hurricanes.gov. 4. The Potential Storm Surge Flooding Map is available on the NHC website. This product depicts a reasonable worst-case scenario - the amount of inundation that has a 10 percent chance of being exceeded at each individual location. Because the Flooding Map is based on inputs that extend out only to about 72 hours, it best represents the flooding potential in those locations within the watch area. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 21.6N 92.6W 30 KT 35 MPH 12H 24/0600Z 22.4N 93.0W 35 KT 40 MPH 24H 24/1800Z 23.8N 93.9W 40 KT 45 MPH 36H 25/0600Z 25.1N 95.2W 50 KT 60 MPH 48H 25/1800Z 26.4N 96.3W 60 KT 70 MPH 72H 26/1800Z 28.6N 97.3W 50 KT 60 MPH...INLAND 96H 27/1800Z 29.0N 97.3W 35 KT 40 MPH...INLAND 120H 28/1800Z 29.0N 96.5W 35 KT 40 MPH...INLAND $$ Forecaster Pasch
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Post-Tropical Cyclone Kenneth Forecast Discussion Number 22
2017-08-23 22:33:36| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Wed Aug 23 2017 000 WTPZ43 KNHC 232033 TCDEP3 Post-Tropical Cyclone Kenneth Discussion Number 22 NWS National Hurricane Center Miami FL EP132017 200 PM PDT Wed Aug 23 2017 Kenneth's organized deep convection has been gone for over 12 hours now. Satellite images also suggest it is losing its tropical character, with some possible frontal structures developing near and northeast of the center. Thus, it no longer meets the requirements of a tropical cyclone, and this is the final advisory. The wind speed is held at 35 kt owing to the tight low-level circulation seen on visible imagery. The post-tropical cyclone should gradually spin down over cold waters and generally move north-northwestward with some decrease in forward speed over the next couple of days. Later in the forecast period, when the cyclone is likely to be very weak and shallow, a turn toward the northwest is expected following the low-level flow. The official track forecast is very close to the previous one. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 25.4N 135.6W 35 KT 40 MPH...POST-TROPICAL 12H 24/0600Z 26.4N 136.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 24/1800Z 27.5N 136.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 25/0600Z 28.1N 136.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 25/1800Z 28.7N 137.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 26/1800Z 30.0N 138.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 27/1800Z 31.2N 139.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 28/1800Z...DISSIPATED $$ Forecaster Blake
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