Here's a quick demo of PyBBIO's BMP183 and HTU21D libraries. This will push temperature, relative humidity, pressure and dew point data to ThingSpeak every 30 seconds.

import requests
from bbio import *
from bbio.libraries.BMP183 import BMP183
from bbio.libraries.HTU21D import HTU21D

bmp = BMP183(SPI0)
htu = HTU21D(I2C2)

API_KEY = "0000000000000000" # Put your write API here

def postData(*data):
  url = "https://api.thingspeak.com/update"
  params = {'api_key' : API_KEY}
  for i in range(0, len(data)):
    params['field%i' % (i+1)] = data[i]
  print params
  response = requests.post(url, params=params)
  print response

def setup():
  pass

def loop():
  pressure = bmp.getPressure() / 1000.0 # in kPa
  rh = htu.getHumidity()
  temp = htu.getTemp()
  dew_point = htu.calculateDewPoint(rh, temp)
  postData(temp, rh, pressure, dew_point)
  delay(30000)

run(setup, loop)

This uses the requests library to send the data to Thingspeak every 30 seconds in HTTP POST requests using the ThingSpeak API. You'll need to create a ThingSpeak channel first, then replace "0000000000000000" with the API key for your channel.

And here's the weather at Gray Cat Labs: https://thingspeak.com/channels/33102/