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Tropical Storm Franklin Forecast Discussion Number 10

2017-08-09 04:54:11| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Tue Aug 08 2017 000 WTNT42 KNHC 090254 TCDAT2 Tropical Storm Franklin Discussion Number 10 NWS National Hurricane Center Miami FL AL072017 1000 PM CDT Tue Aug 08 2017 The center of Franklin moved off the western coast of the Yucatan Peninsula soon after 2100 UTC, and Air Force Reserve and NOAA Hurricane Hunter aircraft arrived not too long after that to begin sampling the cyclone's circulation. The planes have observed increasing deep convection, and the NOAA aircraft measured a peak 700-mb flight-level wind of 52 kt within the convection east of the center. The SFMR instruments have measured surface winds higher than 50 kt, but these values were either rain flagged or likely influenced by shoaling effects in the shallow shelf waters off the Yucatan coast. Accounting for these considerations, Franklin's initial intensity is raised to 45 kt. The Air Force plane also reported that the central pressure has fallen to 996 mb. Franklin is moving west-northwestward, or 285/9 kt, and mid-level ridging located over the northern Gulf of Mexico should force the cyclone to turn westward by Wednesday morning. The track guidance suggests that a south-of-due-west motion is possible after 24 hours as Franklin's circulation interacts with the mountainous terrain of Mexico, and the cyclone's center is expected to cross the coast Wednesday night or early Thursday. The new NHC track forecast is a little south of the previous forecast, accounting for the southward bend noted in the track models. The waters of the Bay of Campeche are around 30 deg C and by themselves should support further intensification. One inhibiting factor for strengthening could be a gradual increase in northerly shear over the system up until landfall, yet many of the intensity models show Franklin intensifying in spite of the shear. In fact, the regional hurricane models depict Franklin reaching an intensity of 70-75 kt in 24 hours. Given that the storm is already producing 45-kt winds after just moving offshore, the NHC forecast lies closer to the more aggressive models and shows Franklin reaching hurricane intensity in about 24 hours. Regardless, there is an increasing likelihood that Franklin will be able to reach hurricane strength before landfall, and accordingly, the government of Mexico has issued a Hurricane Warning for portions of the state of Veracruz. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 20.3N 91.3W 45 KT 50 MPH 12H 09/1200Z 20.4N 93.0W 55 KT 65 MPH 24H 10/0000Z 20.4N 95.1W 65 KT 75 MPH 36H 10/1200Z 20.0N 97.2W 45 KT 50 MPH...INLAND 48H 11/0000Z 19.5N 99.5W 30 KT 35 MPH...INLAND 72H 12/0000Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm Franklin Forecast Discussion Number 9

2017-08-08 22:33:44| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Tue Aug 08 2017 000 WTNT42 KNHC 082033 TCDAT2 Tropical Storm Franklin Discussion Number 9 NWS National Hurricane Center Miami FL AL072017 400 PM CDT Tue Aug 08 2017 Visible satellite images and surface synoptic data indicate that the center of the cyclone is nearing the northwest coast of the Yucatan Peninsula. The overall cloud pattern remains fairly well organized, with distinct banding features and well-defined upper-level outflow. Based on the assumption that only slow weakening has been occurring, the current intensity is set at 35 kt. Franklin should begin to strengthen very soon, when its center moves over the warm waters of the Bay of Campeche. The dynamical guidance indicates that north-northeasterly shear will begin to affect the tropical cyclone when it moves farther west in the southwestern Gulf of Mexico, which should be an impediment for strengthening. The official intensity forecast is above the SHIPS and LGEM guidance but close to the intensity model consensus. Given that it is quite possible that Franklin could become a hurricane by the time of landfall, it is prudent to maintain the Hurricane Watch for the southwest Gulf coast of Mexico. The motion continues west-northwestward or 290/10 kt. A mid-tropospheric high pressure area near the northwestern Gulf coast should cause a generally westward motion over the next couple of days. The official track forecast is similar to the previous ones, and not far from the latest dynamical model consensus. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 20.2N 90.3W 35 KT 40 MPH 12H 09/0600Z 20.5N 91.9W 40 KT 45 MPH...OVER WATER 24H 09/1800Z 20.6N 94.0W 50 KT 60 MPH 36H 10/0600Z 20.7N 96.2W 60 KT 70 MPH 48H 10/1800Z 20.4N 98.2W 30 KT 35 MPH...INLAND 72H 11/1800Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Franklin Forecast Discussion Number 8

2017-08-08 16:33:39| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Tue Aug 08 2017 000 WTNT42 KNHC 081433 TCDAT2 Tropical Storm Franklin Discussion Number 8 NWS National Hurricane Center Miami FL AL072017 1000 AM CDT Tue Aug 08 2017 Franklin's center continues to move over the land mass of the Yucatan Peninsula. Since this area is relatively flat, only slow weakening is likely occurring. The morning sounding from Merida, located over northwest Yucatan, showed winds near 40 kt just above the surface. Assuming that these winds are coming down to the surface somewhere within the circulation, the initial intensity is estimated to be 40 kt. Some additional weakening should occur as long as the center remains over land. A restrengthening trend is forecast to begin when the center moves into the Bay of Campeche later today or tonight. Even though Franklin will be moving over very high SSTs while over the Bay of Campeche, the global models show northerly shear affecting the cyclone as it nears the southwest Gulf coast of Mexico. Although this shear could impede intensification, Franklin could be near hurricane intensity when it nears the coast late Wednesday. Therefore, it is prudent to maintain the Hurricane Watch. The motion continues to be west-northwestward, or 290/11 kt. A mid-tropospheric ridge is forecast to remain in place to the north of Franklin over the next couple of days. This should cause the tropical cyclone to move west-northwestward to westward until its second landfall. The official track forecast is similar to the ECMWF solution and to the previous NHC forecasts. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 19.6N 89.6W 40 KT 45 MPH 12H 09/0000Z 20.0N 91.1W 35 KT 40 MPH...OVER WATER 24H 09/1200Z 20.3N 93.3W 50 KT 60 MPH 36H 10/0000Z 20.4N 95.4W 60 KT 70 MPH 48H 10/1200Z 20.3N 97.6W 50 KT 60 MPH...INLAND 72H 11/1200Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Franklin Forecast Discussion Number 7

2017-08-08 10:56:08| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Tue Aug 08 2017 000 WTNT42 KNHC 080855 TCDAT2 Tropical Storm Franklin Discussion Number 7 NWS National Hurricane Center Miami FL AL072017 400 AM CDT Tue Aug 08 2017 The Belize Doppler weather radar indicates that Franklin's inner-core circulation has tightened up considerably since the previous advisory, likely due to frictional convergence, and that a 10-15-nmi-diameter closed eye has developed. Radar reflectivity values have been steadily increasing in the eyewall, and this development trend is supported by infrared satellite imagery, which shows deep convection with cloud tops of -75C to -80C now completely covering the radar eye. The initial intensity is lowered to 45 kt for this advisory based on a typical decay rate for landfalling tropical cyclones. The initial motion estimate is 290/12 kt, based primarily on radar data. A deep-layer subtropical ridge that currently extends across the northern and central Gulf of Mexico is expected to remain intact through the forecast period, building slightly southward by 48 h and beyond. This entrenched steering pattern is expected to keep Franklin moving west-northwestward across the Yucatan peninsula the next 24 h or so, followed by westward motion across the Bay of Campeche until landfall occurs in 48-60 h. NHC model guidance remains in good agreement on this track scenario, and only a slight nudge to the south of the previous forecast track was required due to the more southward initial position of Franklin. Additional weakening is expected while Franklin moves across the Yucatan peninsula during the next 15 h or so. The recent inner-core structural improvements are expected to remain in place by the time the cyclone emerges over the warm waters of the Bay of Campeche. That, combined with low vertical shear values and a well-established outflow pattern, will allow for restrengthening to occur by Wednesday, possibly resulting in Franklin achieving hurricane status around 36-42 h. However, the GFS and ECMWF models are still forecasting significant northerly vertical shear near 20 kt to develop by 36 h and beyond, which could cap the intensification process or possibly even induce some weakening since mid-level dry air entrainment will accompany the northerly shear. However, since Franklin is expected to be near hurricane strength at landfall, a Hurricane Watch for mainland Mexico is warranted. The new NHC intensity forecast is similar to the previous advisory, and closely follows a blend of the HCCA and IVCN intensity consensus models. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 19.3N 88.5W 45 KT 50 MPH...INLAND 12H 08/1800Z 19.7N 90.2W 35 KT 40 MPH...INLAND 24H 09/0600Z 20.1N 92.4W 50 KT 60 MPH...OVER WATER 36H 09/1800Z 20.3N 94.4W 60 KT 70 MPH 48H 10/0600Z 20.2N 96.6W 60 KT 70 MPH 72H 11/0600Z 19.7N 101.8W 20 KT 25 MPH...INLAND 96H 12/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Franklin Forecast Discussion Number 6

2017-08-08 04:42:07| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Mon Aug 07 2017 000 WTNT42 KNHC 080241 TCDAT2 Tropical Storm Franklin Discussion Number 6 NWS National Hurricane Center Miami FL AL072017 1000 PM CDT Mon Aug 07 2017 Satellite images and radar data from Belize show that Franklin has an expansive and nearly symmetric circulation. However, recent microwave data indicate that the cyclone does not have a well-defined inner core, which is characterized by an elliptical ring of convection that is open on the northwest side. In addition, cloud tops are not very cold near the center, and the deepest convection is located in a band well to the east of the center over the Caribbean Sea. Earlier Hurricane Hunter aircraft data indicated that maximum winds were near 50 kt, and since the satellite presentation has not improved since then, that will remain Franklin's initial intensity. Franklin appears to have turned west-northwestward and sped up just a bit with an initial motion of 300/12 kt. A mid-tropospheric ridge extending across the northern and central Gulf of Mexico should force Franklin west-northwestward and westward across the Yucatan peninsula and into the Bay of Campeche during the next day or two, which is handled well by the numerical models. After 36 hours, there is some latitudinal spread in the track guidance, likely related to how Franklin's circulation interacts with the mountainous terrain of Mexico. Since tropical cyclones in the western Bay of Campeche historically have tended to turn a little southward prior to landfall, the updated NHC track forecast is a little south of the previous forecast, leaning in the direction of the HFIP Corrected Consensus and the GFS. Given Franklin's structure and limited time before landfall, the cyclone is unlikely to strengthen before the center reaches land. Weakening is anticipated while Franklin takes about 18 hours to cross the Yucatan peninsula, but the storm should then begin to restrengthen once it reaches the warm waters of the Bay of Campeche tomorrow evening. It does appear that northerly shear may begin to increase in about 36 hours, but it does not look strong enough to prevent intensification. Continuing the pattern of following the HFIP Corrected Consensus and the ICON intensity consensus, the official forecast shows Franklin reaching hurricane intensity in about 48 hours, and then making landfall on the coast of mainland Mexico as a hurricane between 48 and 72 hours. Despite what is explicitly indicated in the forecast, Franklin's low-level center is likely to dissipate near the mountains of Mexico, with the mid-level remnants continuing westward across central Mexico. Based on the updated forecast, the government of Mexico has discontinued the Hurricane Watch for the east coast of the Yucatan peninsula but has issued a new Hurricane Watch for parts of the state of Veracruz in mainland Mexico. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 19.1N 87.3W 50 KT 60 MPH 12H 08/1200Z 19.7N 88.9W 40 KT 45 MPH...INLAND 24H 09/0000Z 20.2N 91.1W 45 KT 50 MPH...OVER WATER 36H 09/1200Z 20.5N 93.1W 55 KT 65 MPH 48H 10/0000Z 20.6N 95.2W 65 KT 75 MPH 72H 11/0000Z 20.0N 100.4W 30 KT 35 MPH...INLAND 96H 12/0000Z...DISSIPATED $$ Forecaster Berg

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