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Hurricane NORBERT Forecast Discussion Number 9

2014-09-04 16:53:26| National Hurricane Center (East Pacific)

Issued at 800 AM PDT THU SEP 04 2014 000 WTPZ44 KNHC 041453 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 AM PDT THU SEP 04 2014 Norbert has become a little better organized overnight, with the TRMM and AMSR2 microwave sensors indicating that the low- and mid-level centers have become more vertically aligned. The cyclone is still experiencing northeasterly shear though, given the asymmetric shape on the latest satellite images. Dvorak intensity estimates are all near 75 kt, so that will used as the initial wind speed. An Air Force Hurricane Hunter aircraft is en route to investigate Norbert, and should provide a more precise estimate of its intensity. While moderate shear has been affecting the cyclone, it has not been strong enough to prevent slow strengthening. Although the shear is not forecast to change much over the next few days, Norbert is expected to move into an environment characterized by cooler SSTs and drier, more stable air. These negative factors should cause some weakening on Friday, with a more significant downward trend anticipated by late this weekend. The latest NHC forecast is close to a blend of the previous interpolated forecast and the intensity consensus. Norbert should become a remnant low in about 4 days due to it moving over very cool waters west of Baja California. The track of Norbert has been quite erratic over the past 24 hours, but a 12-hour motion still appears to be northwestward at about 6 kt. A mid-level ridge is expected to remain over northwestern Mexico, keeping Norbert on the same general course during the next few days, offshore of Baja California. At long range, model guidance remains divergent on how much of a northward turn that Norbert will take due to a mid-latitude trough weakening the ridge. The 3-5 day track also partially depends on the intensity at that time range, with a deeper system probably moving farther west, more like the ECMWF solution. Since there has not been much change to the overall guidance, the new NHC forecast is about the same as the previous one, and remains relatively close to the dynamical 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 04/1500Z 20.7N 110.4W 75 KT 85 MPH 12H 05/0000Z 21.5N 111.1W 80 KT 90 MPH 24H 05/1200Z 22.5N 112.2W 80 KT 90 MPH 36H 06/0000Z 23.5N 113.3W 75 KT 85 MPH 48H 06/1200Z 24.3N 114.5W 65 KT 75 MPH 72H 07/1200Z 25.9N 117.0W 50 KT 60 MPH 96H 08/1200Z 27.6N 118.6W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 09/1200Z 29.0N 119.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Blake

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Hurricane NORBERT Forecast Discussion Number 8

2014-09-04 10:51:22| National Hurricane Center (East Pacific)

Issued at 200 AM PDT THU SEP 04 2014 000 WTPZ44 KNHC 040851 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 200 AM PDT THU SEP 04 2014 Recent microwave images, including a NASA GPM overpass at 0516 UTC, indicate that Norbert has lost some organization during the past few hours due to easterly vertical wind shear. The low-level center is in the northeastern part of the central convection with a mid-level eye displaced to the southwest of the low-level center. Satellite intensity estimates from TAFB and SAB are unchanged at 77 and 65 kt, and the CIMSS Advanced Dvorak Technique estimates an intensity of 65 kt. Based on these data, the initial intensity remains 70 kt. The microwave data indicate that the center of Norbert made a northward turn since the previous advisory. The initial motion is a somewhat uncertain 325/5. Norbert should continue on a general northwestward motion during the next three days around the southwestern periphery of a mid-level ridge that extends westward across northern Mexico. This part of the forecast track has been nudged to the east based on the current position and motion. After 72 hours, the guidance becomes more divergent due to disagreements in how Norbert interacts with a mid/upper-level trough over the northeastern Pacific. The GFS and NAVGEM forecast Norbert to turn northward, while the ECMWF is forecasting a westward turn and a slower forward speed. The other models are spread between these extremes. The later part of the new track forecast is similar to the previous advisory, and is showing a slow northward motion as a compromise between the extremes. The dynamical models now suggest that moderate shear should continue for the next 24-36 hours, and as a result the intensity guidance shows less strengthening than 6 hours ago. The new intensity forecast is thus nudged downward. Norbert should start weakening by 48 hours as it reaches cooler sea surface temperatures, and the system is forecast to degenerate to a remnant low by the end of the forecast period. The new intensity forecast is in best agreement with the intensity consensus. Moisture indirectly related to Norbert being pulled northward around the eastern side of the cyclone's large circulation is expected to spread across northern Mexico and into the southwestern United States during the next few days. This could result in heavy rains and life-threatening flash flooding in these areas. Please see information from your local weather office for more details. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 20.5N 109.7W 70 KT 80 MPH 12H 04/1800Z 21.2N 110.4W 75 KT 85 MPH 24H 05/0600Z 22.2N 111.4W 80 KT 90 MPH 36H 05/1800Z 23.1N 112.4W 80 KT 90 MPH 48H 06/0600Z 23.9N 113.6W 70 KT 80 MPH 72H 07/0600Z 25.5N 116.0W 55 KT 65 MPH 96H 08/0600Z 27.5N 118.0W 35 KT 40 MPH 120H 09/0600Z 29.0N 119.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Hurricane NORBERT Forecast Discussion Number 7

2014-09-04 04:59:23| National Hurricane Center (East Pacific)

Issued at 800 PM PDT WED SEP 03 2014 000 WTPZ44 KNHC 040259 TCDEP4 HURRICANE NORBERT DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 PM PDT WED SEP 03 2014 Norbert continues to intensify this evening. Evening visible satellite images showed a symmetric central dense overcast feature with curved convective bands wrapping around the center. The latest Dvorak intensity estimates from TAFB, SAB, and UW/CIMMS ADT were between 65 and 77 kt, and the initial wind speed has been increased to 70 kt for this advisory. Norbert is the ninth hurricane to form in the eastern Pacific basin this season. The outflow has become well established, except over the northeastern portion of the cyclone where there is a hint of light to moderate northeasterly shear. However, the shear is not expected to be strong enough to inhibit strengthening during the next day or so while Norbert remains over warm water. The NHC forecast is close to the SHIPS model through 36 h and is similar to the previous advisory. After that time, Norbert will be approaching cooler waters and a drier and more stable airmass, which should cause weakening to commence. A faster rate of weakening is forecast in 48 to 72 hours when the cyclone moves over SSTs below 26C. The hurricane appears to have turned northwestward with an initial motion of 305/7 kt. Norbert should continue on a general northwestward motion during the next several days around the southwestern periphery of a mid-level ridge that extends westward across northern Mexico. The model guidance is in good agreement on the general heading of the cyclone, although there are some differences in the forward speed of Norbert later in the period. Much of the guidance now indicates a faster forward speed late in the period, with the GFS showing a deeper cyclone moving even faster and farther north than the ECMWF, UKMET, and HWRF. The updated NHC track forecast is a little faster than the previous advisory to be in better agreement with the multi-model consensus, but is not nearly as fast as the GFS. Moisture indirectly related to Norbert being pulled northward around the eastern side of cyclone's large circulation is expected to spread across northern Mexico and into the southwestern United States during the next few days. This could result in heavy rains and life-threatening flash flooding in these areas. Please see information from your local weather office for more details. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 19.9N 109.8W 70 KT 80 MPH 12H 04/1200Z 20.7N 110.5W 80 KT 90 MPH 24H 05/0000Z 21.7N 111.4W 85 KT 100 MPH 36H 05/1200Z 22.8N 112.5W 85 KT 100 MPH 48H 06/0000Z 23.7N 113.4W 75 KT 85 MPH 72H 07/0000Z 25.3N 115.5W 55 KT 65 MPH 96H 08/0000Z 27.0N 117.5W 35 KT 40 MPH 120H 09/0000Z 29.0N 118.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Tropical Storm NORBERT Forecast Discussion Number 6

2014-09-03 22:56:53| National Hurricane Center (East Pacific)

Issued at 200 PM PDT WED SEP 03 2014 000 WTPZ44 KNHC 032056 TCDEP4 TROPICAL STORM NORBERT DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 200 PM PDT WED SEP 03 2014 Satellite images indicate that Norbert is still on an intensification trend. While no eye is apparent in visible imagery, recent microwave imagery indicates that an eye is trying to form. The cyclone has a long curved band around the southern and western semicircle wrapping into the small central dense overcast. A blend of the subjective and objective Dvorak estimates gives 60 kt as the initial wind speed. It is hard to find a reason why Norbert will not significantly intensify during the next day or so since it will remain over very warm waters, the shear does not appear to be that detrimental, and it already has many features of an inner core. Yet the best model guidance is lower than 6 hours ago, with no forecast above 80 kt for a peak intensity. With so many favorable environmental factors and the low model bias observed this season (and this cyclone), the new NHC forecast will stay close to the previous one. Weakening should begin in a few days when Norbert moves over cooler waters and into the more stable atmosphere of the subtropical eastern Pacific Ocean. After a brief westward track, Norbert appears to be moving more to the west-northwest, or 300/6. Global models are in good agreement on a weakening ridge over northwestern Mexico forcing the storm to move northwestward over the next few days. Model guidance is well clustered on a track offshore of Baja Califoria Sur, except for the GFDL which has a known northward bias in this region. Norbert is still expected to pass close enough to bring tropical- storm-force winds to portions of the state. The new forecast is a little farther south of the previous one during the first 24 hours, mostly because of the earlier westward motion. Little change has been made to the rest of the forecast, which is just to the west of the dynamical track consensus. Moisture from the combination of Norbert and the remnants of Atlantic Tropical Storm Dolly is expected to spread northwestward across northern Mexico during the next couple of days, and into the southwestern United States over the weekend. Heavy rain causing life-threatening flash flooding are possible in those regions. Please see information from your local weather office for more details. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 19.6N 109.2W 60 KT 70 MPH 12H 04/0600Z 20.1N 110.0W 70 KT 80 MPH 24H 04/1800Z 20.9N 110.8W 85 KT 100 MPH 36H 05/0600Z 21.9N 111.6W 90 KT 105 MPH 48H 05/1800Z 23.0N 112.6W 85 KT 100 MPH 72H 06/1800Z 24.5N 114.5W 65 KT 75 MPH 96H 07/1800Z 26.0N 116.7W 45 KT 50 MPH 120H 08/1800Z 28.0N 118.0W 35 KT 40 MPH $$ Forecaster Blake

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Tropical Storm NORBERT Forecast Discussion Number 5

2014-09-03 16:44:18| National Hurricane Center (East Pacific)

Issued at 800 AM PDT WED SEP 03 2014 000 WTPZ44 KNHC 031444 TCDEP4 TROPICAL STORM NORBERT DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 AM PDT WED SEP 03 2014 Norbert has become significantly better organized this morning. The central dense overcast has become more symmetric with more prominent banding around the center. Microwave images also show that the inner core is becoming better defined, with the likely first stages of a primitive eye. The initial wind speed is set to 55 kt, at the top end of the subjective Dvorak estimates, although the latest objective numbers are higher. With the improvement in the inner core, light-to-moderate shear, and very warm waters, future strengthening seems quite likely. In fact, rapid intensification is a distinct possibility, with the SHIPS-RI showing about a 1-in-3 chance of Norbert becoming 30 kt stronger in the next 24 hours. Considering the environmental factors and the low bias of the deterministic guidance so far, the new NHC intensity forecast is raised considerably from the previous one, about 5 kt above the highest guidance through 48 hours. After that time, cooler waters and a more stable atmosphere are expected to weaken the cyclone. The NHC forecast is blended with the previous forecast and the intensity consensus at long range. With recent microwave and visible imagery, it appears that Norbert has been moving westward over the past few hours. However, a more representative long-term motion is 295/8. Mid-level ridging is expected to weaken later today over northwestern Mexico, which should cause Norbert to turn more to the northwest. While all of the reliable guidance keeps the center of the storm offshore of Baja California Sur, Norbert should come close enough to bring tropical- storm-force winds to the state. The models have shifted somewhat southward since the last cycle, and with the recent westward motion, it makes sense to adjust the NHC forecast a little farther south for the first day or so. There hasn't been much change to the guidance beyond day 3, so the new forecast is basically an update to the previous one. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 19.6N 108.8W 55 KT 65 MPH 12H 04/0000Z 20.1N 109.6W 65 KT 75 MPH 24H 04/1200Z 20.9N 110.3W 80 KT 90 MPH 36H 05/0000Z 21.8N 111.0W 90 KT 105 MPH 48H 05/1200Z 22.6N 111.9W 90 KT 105 MPH 72H 06/1200Z 24.4N 113.9W 70 KT 80 MPH 96H 07/1200Z 25.6N 116.2W 55 KT 65 MPH 120H 08/1200Z 27.0N 117.5W 40 KT 45 MPH $$ Forecaster Blake

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