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Tropical Storm Ivo Forecast Discussion Number 8
2019-08-23 10:42:29| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Fri Aug 23 2019 000 WTPZ45 KNHC 230842 TCDEP5 Tropical Storm Ivo Discussion Number 8 NWS National Hurricane Center Miami FL EP102019 300 AM MDT Fri Aug 23 2019 Unexpectedly, stronger than anticipated northeasterly shear affected Ivo during the past 12 hours or so, and the low-level center became detached from the main area of deep convection. The center can be clearly seen on microwave and conventional imagery, and it is located very near Clarion Island, Mexico. An automatic Mexican Navy weather station at that location reported that the surface pressure has been falling and has measured gusts to 39 kt. This information is very valuable to diagnose the structure of the cyclone. Despite the deterioration of the cloud pattern, a recent ASCAT pass measured a peak wind of 50 kt associated with Ivo, but this value was confined to a small area in the southeast quadrant. On this basis, the initial intensity has been adjusted downward to 50 kt, which is also a value close to the Dvorak estimates, or perhaps a tad higher. The cyclone is expected to be over warm waters for about a day or so, and given its vigorous circulation, Ivo could maintain the same intensity for the next 12 hours. After that time, Ivo should begin to weaken over cooler waters. Unanimously, all the models weaken the cyclone and so does the NHC forecast, and by 72 hours or sooner, Ivo should have degenerated into a remnant low. The center is moving toward the north-northwest or 330 degrees at 9 kt. The cyclone managed to find a weakness in the ridge, and since the steering pattern is not expected to change, this general motion is anticipated to continue until dissipation in 4 days. The NHC forecast is on the left edge of the guidance envelope and is basically on top of the multi-model consensus TVCE. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 17.9N 114.5W 50 KT 60 MPH 12H 23/1800Z 19.0N 115.2W 50 KT 60 MPH 24H 24/0600Z 20.5N 116.1W 45 KT 50 MPH 36H 24/1800Z 22.0N 116.8W 40 KT 45 MPH 48H 25/0600Z 24.0N 117.5W 30 KT 35 MPH 72H 26/0600Z 27.5N 119.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 27/0600Z...DISSIPATED $$ Forecaster Avila
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Tropical Depression Chantal Forecast Discussion Number 10
2019-08-23 10:38:56| National Hurricane Center (Atlantic)
Issued at 500 AM AST Fri Aug 23 2019 000 WTNT44 KNHC 230838 TCDAT4 Tropical Depression Chantal Discussion Number 10 NWS National Hurricane Center Miami FL AL042019 500 AM AST Fri Aug 23 2019 Chantal's convection has become quite meager, with small intermittent bursts continuing mainly to the east of the center. Given the decreasing convective organization, Dvorak Current Intensity numbers from TAFB and SAB are down to 1.5, and the initial intensity is therefore lowered to 25 kt. Large-scale subsidence and a very dry air mass are making it harder and harder for Chantal to maintain organized deep convection, and it's likely that the depression will degenerate into a remnant low within the next 24 hours. Each of the global models shows the remnant low hanging around for various periods of time, but the official forecast continues to show dissipation in 72 hours, which is in closest agreement with the ECMWF model. Chantal is moving southeastward, or 140/7 kt. High pressure in the lower levels of the atmosphere is expected to jump from the southwest to the northeast of Chantal during the next couple of days, which will cause the depression/remnant low to move slowly southward and then westward before dissipating. The latest track guidance (and thus the official forecast) shows a more sweeping curved trajectory than before, but in the grand scheme of things the change is not that significant. The new NHC forecast generally lies between the TVCX and HCCA consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 37.1N 40.9W 25 KT 30 MPH 12H 23/1800Z 36.3N 40.7W 25 KT 30 MPH 24H 24/0600Z 35.4N 41.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 24/1800Z 35.2N 42.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 25/0600Z 35.4N 43.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 26/0600Z...DISSIPATED $$ Forecaster Berg
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Tropical Depression Chantal Forecast Discussion Number 9
2019-08-23 04:34:24| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Thu Aug 22 2019 000 WTNT44 KNHC 230234 TCDAT4 Tropical Depression Chantal Discussion Number 9 NWS National Hurricane Center Miami FL AL042019 1100 PM AST Thu Aug 22 2019 Chantal continues to survive the harsh thermodynamic and shear environment of the central Atlantic by producing intermittent small bursts of deep convection well to the east of the exposed surface center. No changes to the subjective satellite intensity estimates from TAFB and SAB this evening, and the initial intensity is once again held at 30 kt. Large-scale sinking air with low to mid-level associated relative humidities less than 40 percent along with increasing west-southwesterly vertical shear are expected to weaken Chantal to a remnant low by Saturday, and dissipate in less than 3 days. The initial motion is estimated to be southeastward, or 135/6 kt, around the northeastern periphery of a subtropical ridge over the central Atlantic. The global and ensemble guidance continue to show an anti-cyclonic motion at a slower forward speed before the system dissipates over the weekend. The new NHC forecast follows suit and is based on a compromise of the NOAA HCCA model and the simple TVCA multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 37.8N 41.9W 30 KT 35 MPH 12H 23/1200Z 37.1N 41.2W 30 KT 35 MPH 24H 24/0000Z 36.1N 41.3W 30 KT 35 MPH 36H 24/1200Z 35.6N 42.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 25/0000Z 35.9N 42.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 26/0000Z...DISSIPATED $$ Forecaster Roberts
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Tropical Storm Ivo Forecast Discussion Number 7
2019-08-23 04:32:53| National Hurricane Center (East Pacific)
Issued at 900 PM MDT Thu Aug 22 2019 885 WTPZ45 KNHC 230232 TCDEP5 Tropical Storm Ivo Discussion Number 7 NWS National Hurricane Center Miami FL EP102019 900 PM MDT Thu Aug 22 2019 Visible satellite pictures show that the center of Ivo has become exposed to the northeast of the deep convection due to moderate to strong northeasterly shear. Although the latest Dvorak T-numbers have decreased slightly, the initial intensity is being held at 55 kt which is in agreement with earlier ASCAT data and recent UW/CIMSS SATCON estimates. Overnight scatterometer data should provide a better assessment of Ivo's intensity. Guidance suggests that the shear is likely to remain moderate to strong during the next 12-18 hours while Ivo traverses warm waters. The shear could relax Friday night, but by that time the cyclone is forecast to move over decreasing SSTs and into a less favorable thermodynamic environment. As a result, little overall change in strength is anticipated during the next day or so. After that time, Ivo should weaken as it moves over SSTs below 26C and into a stable air mass. The cyclone is forecast to become a remnant low within 72 hours, and dissipate by day 5. Ivo has turned sharply today, with the initial motion now north-northwestward or 335/8 kt. The storm is forecast to move northwestward to north-northwestward around the western side of a mid-level ridge. The latest track envelope has shifted eastward, partially due to the sharper turn and the more eastward initial position. This has resulted in a slightly eastward shift in the official forecast, but it remains close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 16.9N 114.1W 55 KT 65 MPH 12H 23/1200Z 18.0N 115.0W 55 KT 65 MPH 24H 24/0000Z 19.5N 115.9W 55 KT 65 MPH 36H 24/1200Z 21.2N 116.8W 50 KT 60 MPH 48H 25/0000Z 23.0N 117.6W 40 KT 45 MPH 72H 26/0000Z 26.6N 119.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 27/0000Z 28.5N 120.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 28/0000Z...DISSIPATED $$ Forecaster Brown
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Tropical Storm Ivo Forecast Discussion Number 6
2019-08-22 22:33:00| National Hurricane Center (East Pacific)
Issued at 300 PM MDT Thu Aug 22 2019 000 WTPZ45 KNHC 222032 TCDEP5 Tropical Storm Ivo Discussion Number 6 NWS National Hurricane Center Miami FL EP102019 300 PM MDT Thu Aug 22 2019 Visible satellite images show a bit of a surprise with Ivo this afternoon. The system is not as well organized as earlier microwave data displayed, with the center almost partially exposed on the northeastern side of the central dense overcast. The initial wind speed is held at 55 kt, which is in line with TAFB/SAB estimates and 50-55 kt ASCAT-C winds. With shear still forecast to increase overnight, only slight intensification of Ivo is anticipated. While Ivo could still become a hurricane, almost all of the guidance has backed off on this cycle. Weakening should begin over the weekend when the storm moves over progressive cooler waters. Convection is likely to dissipate in about 72 hours, and post-tropical status of Ivo is forecast at that time. Overall the new forecast is reduced about 5 kt from the previous one, near or slightly above the model consensus. Ivo has turned west-northwestward, or 295/8 kt. The storm should turn to the northwest tomorrow and north-northwest on Saturday due to steering from a mid-level ridge over Mexico. Model guidance is coming into better agreement on this course, with fairly small variations. Overall, the small eastward trend seen in the guidance continues, and the new NHC prediction is shifted a little eastward at long range. Still, none of the guidance still show a direct tropical cyclone threat to Mexico at this time. It is worth noting that the current size of Ivo has been greatly increased due to the ASCAT-C data. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 16.1N 114.1W 55 KT 65 MPH 12H 23/0600Z 17.0N 114.9W 60 KT 70 MPH 24H 23/1800Z 18.5N 116.0W 60 KT 70 MPH 36H 24/0600Z 20.2N 116.9W 55 KT 65 MPH 48H 24/1800Z 22.0N 117.8W 45 KT 50 MPH 72H 25/1800Z 25.9N 119.7W 35 KT 40 MPH...POST-TROPICAL 96H 26/1800Z 28.5N 121.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 27/1800Z...DISSIPATED $$ Forecaster Blake
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