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Hurricane NORBERT Forecast Discussion Number 16

2014-09-06 10:50:36| National Hurricane Center (East Pacific)

Issued at 200 AM PDT SAT SEP 06 2014 000 WTPZ44 KNHC 060850 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 200 AM PDT SAT SEP 06 2014 Norbert continued to rapidly intensify through about 06Z. Since then, the hurricane appears to have peaked in intensity, with the eye becoming less distinct and the cold cloud tops in the eyewall becoming asymmetric. Satellite intensity estimates at 06Z were 115 kt from TAFB and 102 kt from SAB, while the CIMMS ADT estimates peaked at 110 kt. Based on these data, the initial intensity is increased to 105 kt as a compromise between these estimates and the decay of the cloud pattern since 06Z. The initial motion is now 315/7. The track forecast reasoning remains unchanged, as Norbert will be steered around the western periphery of a mid-level ridge centered over the southern United States through 48 hours. After that time, the ridge weakens as a mid-latitude trough moves into the U.S. West Coast, which should result in a weakening of the steering currents. The track guidance has come into better agreement that Norbert should move northeastward or eastward after 72 hours, with several of the models showing the remnants making landfall over the northern portion of the Baja California peninsula. The new forecast track reflects this change in the guidance by showing an northeastward and eastward drift after 72 hours. The new forecast track is a little to the right of the center of the guidance envelope through 48 hours, and after that it is slower than the consensus model TVCE. The forecast track takes Norbert over steadily decreasing sea surface temperatures. The cyclone should thus weaken through the forecast period. Despite the higher initial intensity compared to 6 hours ago, the guidance is in good agreement that Norbert should decay into a remnant low in about 3 days. The new intensity forecast is increased from that of the previous forecast through 36 hours, and then is similar to the previous forecast. The new forecast is in best agreement with the LGEM 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 06/0900Z 24.6N 113.4W 105 KT 120 MPH 12H 06/1800Z 25.2N 114.4W 100 KT 115 MPH 24H 07/0600Z 26.0N 115.6W 85 KT 100 MPH 36H 07/1800Z 26.9N 116.6W 65 KT 75 MPH 48H 08/0600Z 27.8N 117.2W 50 KT 60 MPH 72H 09/0600Z 29.5N 117.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 10/0600Z 30.0N 116.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 11/0600Z 30.0N 116.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Hurricane NORBERT Forecast Discussion Number 14

2014-09-05 22:41:34| National Hurricane Center (East Pacific)

Issued at 200 PM PDT FRI SEP 05 2014 000 WTPZ44 KNHC 052041 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 200 PM PDT FRI SEP 05 2014 Even though Norbert's cloud pattern remains fairly well organized in satellite imagery, cloud top temperatures in the central dense overcast have been slowly warming since this morning. Nevertheless, an Air Force Reserve Unit Hurricane Hunter aircraft reported maximum flight-level winds of 92 kt and peak SFMR winds of 76 kt in the northeastern quadrant, with a minimum pressure of 966 mb. These data support an initial intensity estimate of 80 kt for this advisory. While Norbert will be moving over above-normal SSTs of 27-29 deg C west of the southern Baja California peninsula during the next day or so, some northeasterly shear and an influx of drier and more stable air over the western part of circulation should contribute to a slow weakening. After that time, Norbert should reach substantially cooler waters and other thermodynamic variables should become much less favorable. These negative factors should result in a near-rapid weakening of the cyclone in 2-3 days, and remnant low status is forecast in 3 days. Encountering even cooler waters on day 4-5 and an increase in shear, Norbert should spin down further and dissipate just beyond the end of the forecast period. The NHC intensity forecast has not changed from the previous one and is near the multi-model consensus IVCN. Satellite and aircraft fixes indicate an initial motion toward the northwest or 325/7 kt. Some re-building of the mid-level ridge to the north of Norbert should cause a slight bend of the track toward the left during the next day or two. After that time, Norbert is expected to reach the western edge of the ridge and encounter a weakness caused by a mid-latitude trough advancing eastward from offshore of the California coast. This synoptic pattern should result in a gradual northward turn during with some decrease in forward speed. The mid-level center of the cyclone is likely to move rapidly northeastward into the southwestern United States on days 3-4, leaving the low-level center meandering offshore the west- central Baja California peninsula until dissipation. The NHC forecast track is little changed from the previous one, and lies on the far eastern side of the guidance envelope and east of the multi- model consensus TVCE. The hurricane-force wind radii have expanded in the northeastern quadrant based on SFMR data from the aircraft and now extend out 40 n mi from the center. Any deviation to the right of the forecast track would bring hurricane conditions onshore in the hurricane warning area. 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 05/2100Z 23.6N 112.2W 80 KT 90 MPH 12H 06/0600Z 24.3N 113.3W 75 KT 85 MPH 24H 06/1800Z 25.0N 114.4W 70 KT 80 MPH 36H 07/0600Z 25.8N 115.6W 60 KT 70 MPH 48H 07/1800Z 26.5N 116.6W 45 KT 50 MPH 72H 08/1800Z 28.4N 117.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 09/1800Z 29.2N 117.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 10/1800Z 29.5N 117.4W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ Forecaster Kimberlain

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Hurricane NORBERT Forecast Discussion Number 13

2014-09-05 16:54:32| National Hurricane Center (East Pacific)

Issued at 800 AM PDT FRI SEP 05 2014 000 WTPZ44 KNHC 051454 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 AM PDT FRI SEP 05 2014 The cloud pattern continues to be fairly well organized with a large area of deep convection near the center and an eye feature noted in microwave data. Objective and subjective Dvorak T-numbers have changed little and still support an initial intensity of 80 kt. Norbert is moving over an area of above normal sea surface temperatures and within an environment of low shear, so there is no reason for the cyclone to change much in intensity today. After that time, the circulation will gradually begin to move over cooler waters and into a more stable environment, resulting in a gradual weakening. Norbert's slow motion over cold water parallel to the Baja California Peninsula will tend to limit the cyclone's impact north of the current warning area. The new NHC forecast is similar to the previous one and follows the intensity consensus ICON. Norbert has been wobbling during the past 12 to 24 hours, but the average motion is toward the northwest or 320 degrees at 7 kt. The cyclone is expected to continue on this general track around the mid-level ridge over Mexico for the next 2 to 3 days. Thereafter, the steering currents are forecast to weaken as a trough in the westerlies swings by to the north of Norbert. The cyclone should then slow down and begin to meander. There is high confidence in the first 3 days of the forecast since guidance is tightly clustered. After that time, there is less confidence due to the large spread in model tracks, but the general trend is either little motion or a slow turn toward the northeast. By then, Norbert is expected to be a weak tropical storm or a remnant low. 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 05/1500Z 23.2N 112.1W 80 KT 90 MPH 12H 06/0000Z 24.1N 113.0W 75 KT 85 MPH 24H 06/1200Z 25.0N 114.2W 70 KT 80 MPH 36H 07/0000Z 25.8N 115.4W 65 KT 75 MPH 48H 07/1200Z 26.5N 116.5W 45 KT 50 MPH 72H 08/1200Z 28.0N 118.0W 35 KT 40 MPH 96H 09/1200Z 29.0N 118.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 10/1200Z 30.0N 118.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Avila

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Hurricane NORBERT Forecast Discussion Number 11

2014-09-05 04:50:56| National Hurricane Center (East Pacific)

Issued at 800 PM PDT THU SEP 04 2014 000 WTPZ44 KNHC 050250 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 PM PDT THU SEP 04 2014 The satellite presentation of the hurricane has not changed much during the past several hours. There has been no evidence of an eye in either geostationary or recent microwave images, however the central dense overcast remains fairly symmetric with cloud tops colder than -80C. Subjective and objective Dvorak estimates remain unchanged and the initial wind speed is kept at 80 kt. The hurricane has likely peaked in intensity and some slight weakening is predicted during the next 24 hours while the large circulation interacts with land and begins to ingest some drier and more stable air from the west. After that time, Norbert is forecast to move over progressively cooler waters and into a less favorable thermodynamic environment. This should lead to a faster rate of weakening and Norbert is predicted to become a remnant low in about 4 days. The NHC intensity forecast is close to the SHIPS/LGEM models during the first day or so, and in good agreement with the intensity consensus thereafter. Recent satellite fixes indicate that Norbert is moving north- northwestward or 330/7 kt. The cyclone is expected to move generally northwestward around the southwestern portion of a mid-level ridge over northern Mexico during the next few days. The model guidance has once again shifted eastward during the first 48 hours, which has required another eastward adjustment to the NHC track. Although none of the guidance models show the center of Norbert crossing the coast of the Baja peninsula, the eastward shift means that the core of the hurricane is likely to pass closer to portions of the Pacific coast of Baja. Only a slight deviation to the right of the track would bring hurricane-force winds to the coast. As a result, the government of Mexico has issued a Hurricane Warning for a portion of the Pacific coast of the Baja peninsula. As noted in the previous discussion, large spread remains in the track guidance after 72 hours, and the NHC track lies near the multi-model consensus at days 4 and 5. 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 05/0300Z 22.0N 111.1W 80 KT 90 MPH 12H 05/1200Z 22.9N 111.8W 75 KT 85 MPH 24H 06/0000Z 23.9N 112.8W 70 KT 80 MPH 36H 06/1200Z 24.8N 113.9W 65 KT 75 MPH 48H 07/0000Z 25.7N 115.2W 55 KT 65 MPH 72H 08/0000Z 27.1N 117.3W 35 KT 40 MPH 96H 09/0000Z 28.5N 118.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 10/0000Z 29.0N 118.8W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Hurricane NORBERT Forecast Discussion Number 10

2014-09-04 22:57:55| National Hurricane Center (East Pacific)

Issued at 200 PM PDT THU SEP 04 2014 000 WTPZ44 KNHC 042057 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 200 PM PDT THU SEP 04 2014 Norbert has changed little on satellite images today, with the central dense overcast remaining fairly solid, and only faint hints of an eye. An Air Force Reserve Hurricane Hunter Aircraft found maximum 700 mb winds of 84 kt, with peak SFMR values of 78 kt. These data support an initial intensity of 80 kt for this advisory, which happen to correspond well to a blend of all the currently available Dvorak estimates. The hurricane is probably near its peak intensity since it will soon move over somewhat cooler SSTs and become more influenced by drier stable air from the subtropical eastern Pacific waters. Model guidance is in fairly good agreement on the cyclone gradually losing strength over the next few days, and little change has been made to the previous forecast, which remains close to the model consensus. The cyclone is expected to transition into a remnant low in about 4 days when it moves over waters cooler than 24C. Norbert is moving northwestward at about 7 kt. A mid-level ridge is expected to persist over northwestern Mexico, keeping Norbert on the same general course during the next few days. Model guidance has shifted a bit closer to the southern Baja California peninsula during the first couple of days, but all of the guidance keeps the center a relatively safe distance offshore. Thereafter, the key to the long range forecast appears to be how much ridging rebuilds in over northwestern Mexico in the wake of a weak shortwave. The ECMWF and the UKMET have a stronger ridge, which keeps Norbert, or its remnants, farther offshore of southern California. The GFS-based guidance moves Norbert closer to northwestern Mexico or southern California, mostly due to a weaker ridge. The dynamical model consensus has changed little during the past few cycles, so I have elected to keep the previous forecast almost the same at days 4-5, which is just a bit south of the latest consensus aids. 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 04/2100Z 21.2N 110.8W 80 KT 90 MPH 12H 05/0600Z 22.0N 111.5W 80 KT 90 MPH 24H 05/1800Z 23.0N 112.5W 75 KT 85 MPH 36H 06/0600Z 23.9N 113.5W 70 KT 80 MPH 48H 06/1800Z 24.8N 114.7W 60 KT 70 MPH 72H 07/1800Z 26.4N 117.0W 45 KT 50 MPH 96H 08/1800Z 28.1N 118.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 09/1800Z 29.0N 119.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Blake

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