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Tropical Storm NORBERT Forecast Discussion Number 21

2014-09-07 16:33:43| National Hurricane Center (East Pacific)

Issued at 800 AM PDT SUN SEP 07 2014 000 WTPZ44 KNHC 071433 TCDEP4 TROPICAL STORM NORBERT DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 AM PDT SUN SEP 07 2014 Deep convection has been decreasing quickly during the last several hours, and only a small area of cold cloud tops remains to the south of the center. Satellite intensity estimates are falling, and the initial wind speed is lowered to 50 kt using an average of the Dvorak CI-numbers from TAFB, SAB, and UW-CIMSS. The quick weakening of Norbert is due to the influence of cool waters of around 25 C and a dry stable air mass. These factors will become even more unfavorable along the expected track of Norbert, and should cause the cyclone to degenerate to a remnant low in about 24 hours, or maybe even sooner. Once Norbert becomes a remnant low, the cyclone is expected to slowly spin down and then open into a trough in about 4 days. The NHC intensity forecast is lower than the previous one, mainly due to the observed rate of weakening. Norbert is still moving west-northwestward, but it is expected to turn toward the northwest and then north during the next day or so when it feels the influence of a deep-layer trough west of California. A slow down and turn toward the northeast or east is expected after that time when the shallow system is steered by the low-level flow toward the Baja California peninsula. No significant change was made to the previous track forecast, and it lies close to the GFS/ECMWF consensus. Although the system is weakening quickly, tropical moisture associated with Norbert and the Pacific ITCZ will continue to spread northward across northern Mexico and the southwestern United States. This could result in heavy rains and life-threatening flash flooding in these area during the next day or two. Please see information from your local weather office for more details. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 26.0N 117.0W 50 KT 60 MPH 12H 08/0000Z 26.9N 117.7W 35 KT 40 MPH 24H 08/1200Z 27.9N 118.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 09/0000Z 28.5N 118.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 09/1200Z 29.1N 117.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 10/1200Z 29.5N 116.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 11/1200Z...DISSIPATED $$ Forecaster Cangialosi

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Hurricane NORBERT Forecast Discussion Number 20

2014-09-07 10:42:22| National Hurricane Center (East Pacific)

Issued at 200 AM PDT SUN SEP 07 2014 000 WTPZ44 KNHC 070842 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 200 AM PDT SUN SEP 07 2014 Deep convection has continued to decrease significantly since the previous advisory, and only a small area of thunderstorms exists near the center and in the southeastern quadrant now. Due to the rapid erosion of the convection, satellite intensity estimates have sharply decreased, and the initial intensity of 65 kt is a conservative blend of the TAFB, SAB, and UW-CIMSS ADT estimates. Norbert's initial motion estimate is 290/08, a little to the left of the previous advisory motion. No significant changes were made to the previous forecast track, and the forecast philosophy remains basically unchanged. During the next 72 hours, Norbert is expected to move slowly northwestward and then northward around the western periphery of a deep-layer ridge located over the southwestern United States. As the cyclone weakens over colder water, the low-level circulation is expected to remain behind to the west of the high mountain ranges across northern Baja California, while the mid- and upper-level circulation decouples and moves northeastward into the southwestern United States. The official track forecast is similar to the previous advisory track, and closely follows the multi-model consensus TVCE. Norbert is currently located over sub-26C sea-surface temperatures, and the cyclone will be moving over even colder water and into a drier and more stable air mass during the next 72 hours. The result is that rapid weakening is forecast during the next 24 hours, with Norbert becoming a non-convective remnant low to the west of the northern Baja California Peninsula in 36 hours or so. The NHC intensity forecast is close the latest IVCN multi-model consensus and follows the rapid weakening trend indicated by the SHIPS model. Moisture from the remnants of Dolly and the Pacific ITCZ is being advected northward by the outer circulation of Norbert across northern Mexico and into the southwestern United States. This could result in heavy rains and life-threatening flash flooding in these areas during the next few days. Please see information from your local weather office for more details. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 25.7N 116.4W 65 KT 75 MPH 12H 07/1800Z 26.4N 117.1W 50 KT 60 MPH 24H 08/0600Z 27.4N 117.8W 40 KT 45 MPH 36H 08/1800Z 28.3N 118.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 09/0600Z 29.0N 117.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 10/0600Z 29.7N 116.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 11/0600Z 29.7N 116.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 12/0600Z...DISSIPATED $$ Forecaster Stewart

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Hurricane NORBERT Forecast Discussion Number 19

2014-09-07 04:34:10| National Hurricane Center (East Pacific)

Issued at 800 PM PDT SAT SEP 06 2014 000 WTPZ44 KNHC 070234 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 PM PDT SAT SEP 06 2014 The cloud pattern of Norbert has degraded significantly over the past few hours. The eye is no longer apparent, and in fact there is no deep convection north of the center where SSTs are below 26C. Satellite intensity estimates continue to decrease, and the initial intensity of 75 kt is based on the latest UW-CIMSS ADT estimate and the Dvorak estimate from SAB. Rapid weakening is expected to continue during the next 24 hours, as the cyclone will move over colder waters and into a drier and more stable environment. Norbert should then weaken more slowly to remnant low status in 2 to 3 days over the cold waters west of the northern Baja California peninsula. The new NHC intensity forecast is close the latest IVCN multi-model consensus. Norbert has jogged a bit to the left over the past few hours, with an initial motion estimate of 300/07. The synoptic reasoning for the track forecast remains unchanged. Norbert will be steered around the southwestern periphery of a mid-level ridge centered over the southwestern United States, which should result in a turn toward the north-northwest by 24 hours. By 48 hours, Norbert should turn northward as it moves into a break in the ridge at the base of a mid-latitude trough off the U.S. West Coast. A slow northeastward motion is shown late in the period as the shallow cyclone will be embedded in weak low-level flow. The new NHC track is similar to the previous one adjusted for the initial position and motion. The 34-kt wind radii have been adjusted inward based on data from a recent ASCAT-B pass. Moisture from the remnants of Dolly and the Pacific ITCZ is being advected northward by the outer circulation of Norbert across northern Mexico and into the southwestern United States. This could result in heavy rains and life-threatening flash flooding in these areas during the next few days. Please see information from your local weather office for more details. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 25.5N 115.5W 75 KT 85 MPH 12H 07/1200Z 25.9N 116.3W 60 KT 70 MPH 24H 08/0000Z 26.9N 117.0W 45 KT 50 MPH 36H 08/1200Z 27.9N 117.6W 35 KT 40 MPH 48H 09/0000Z 28.8N 117.6W 30 KT 35 MPH 72H 10/0000Z 29.7N 116.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 11/0000Z 30.0N 116.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 12/0000Z...DISSIPATED $$ Forecaster Brennan

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Hurricane NORBERT Forecast Discussion Number 18

2014-09-06 22:39:10| National Hurricane Center (East Pacific)

Issued at 200 PM PDT SAT SEP 06 2014 000 WTPZ44 KNHC 062039 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 200 PM PDT SAT SEP 06 2014 The eye continues to be evident on visible images, but the convection is not as deep as it was earlier. In fact, the strongest convection is limited to the southern semicircle where the ocean is still warm. Dvorak T-numbers have continued to decrease, and based on blend of these estimates, the initial intensity has been lowered to 90 kt. The northern portion of the circulation is already reaching cooler waters and moving into a more stable environment. This should result in steady or even rapid weakening during the next 24 hours, with a slower rate of weakening thereafter as the circulation gradually spins down. Norbert is expected to become a remnant low over the cold waters just west of the northern Baja California peninsula in 3 days or so. Norbert has been moving toward the northwest or 305 degrees at 7 knots. It is not necessary to make any significant adjustment to the previous forecast track since the global models are not showing any changes in the steering flow. As indicated earlier, Norbert is forecast to move with the flow around the southwestern periphery of a mid-level ridge centered over the southwestern United States. In 48 hours, the cyclone will reach the base of the mid-latitude westerlies and begin to move northward and then northeastward. By then, Norbert is forecast to be a shallow cyclone and will be moving little in a weak low-level flow. The NHC forecast follows the trend indicated by the multi-model consensus. Moisture from the remnants of Dolly and the Pacific ITCZ is being advected northward by the outer circulation of Norbert across northern Mexico and into the southwestern United States. This could result in heavy rains and life-threatening flash flooding in these areas during the next few days. Please see information from your local weather office for more details. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 25.3N 114.8W 90 KT 105 MPH 12H 07/0600Z 25.8N 115.9W 75 KT 85 MPH 24H 07/1800Z 26.6N 116.8W 55 KT 65 MPH 36H 08/0600Z 27.5N 117.5W 40 KT 45 MPH 48H 08/1800Z 28.8N 117.8W 35 KT 40 MPH 72H 09/1800Z 29.5N 117.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 10/1800Z 30.0N 116.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 11/1800Z...DISSIPATED $$ Forecaster Avila

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Hurricane NORBERT Forecast Discussion Number 17

2014-09-06 16:34:39| National Hurricane Center (East Pacific)

Issued at 800 AM PDT SAT SEP 06 2014 000 WTPZ44 KNHC 061434 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 AM PDT SAT SEP 06 2014 First visible images reveal a pinhole eye surrounded by very deep convection. Nevertheless, after a rapid intensification observed on satellite last night, objective and subjective Dvorak T-numbers are decreasing, and only support an initial intensity of 100 kt. A portion of the circulation is already reaching cooler waters and moving into a more stable environment. This should result in a gradual weakening during the next 24 hours, with a faster rate of weakening thereafter. Norbert is expected to become a remnant low over the cold waters just west of the northern Baja California peninsula in 3 days or so. The best estimate of the initial motion is toward the northwest or 310 degrees at 7 knots. Norbert is forecast to be steered by the flow around the southwestern periphery of a mid-level ridge centered over the southwestern United States. In a 48 hours, the cyclone will reach the base of the mid-latitude westerlies and will begin to move northward and then northeastward. By then, Norbert is forecast to be a shallow cyclone, moving little in a weak low-level flow. There is high confidence in the short- term track forecast since there is a good guidance agreement. Beyond 3 days, global models either forecast Norbert to dissipate in situ near the west coast of the northern Baja California peninsula or continue to move the system eastward as a weak low or a trough. The NHC prefers the former global model solution. Moisture from the remnants of Dolly and the Pacific ITCZ is being advected northward by the outer circulation of Norbert across northern Mexico and into the southwestern United States. This could result in heavy rains and life-threatening flash flooding in these areas during the next few days. Please see information from your local weather office for more details. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 25.0N 114.1W 100 KT 115 MPH 12H 07/0000Z 25.6N 115.1W 80 KT 90 MPH 24H 07/1200Z 26.5N 116.4W 65 KT 75 MPH 36H 08/0000Z 27.3N 117.3W 50 KT 60 MPH 48H 08/1200Z 28.2N 117.8W 40 KT 45 MPH 72H 09/1200Z 29.5N 117.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 10/1200Z 30.0N 116.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 11/1200Z 30.0N 116.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Avila

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